Conference PaperPDF Available

Experimental study of earth batteries

Authors:

Abstract and Figures

We report successful design, construction and operation of an earth battery as an alternate energy source for low power electric supply applications. Different combinations of metallic and non-metallic solid, liquid and gas electrodes were investigated for maximum potential difference. In view of robust and cost effective use of this natural power technology by unskilled village consumers most suitable combinations of the commonly available metals were selected for further detailed characteristic studies. Combinations of Magnesium anode and Coke cathode; Zinc anode and Graphite cathode; Aluminum anode and Carbon cathode; Zinc anode and Copper cathodes gave 2.05, 1.40, 1.10 and 0.9 volts per cell. Typical rated power of a single Zn-Cu cell was measured to be few tens of microamperes. Small power electronic devices such as calculators, electronic watches, baby toys and cell phones and white light LEDs were operated on site. The voltage level was found to increase linearly by connecting multiple earth battery cells in series like commercial lead acid battery. The load current was found to increase by connecting earth cells in parallel. The source current capacities were also found to increase by increasing surface areas of the electrodes. However, single cell voltage was found to remain constant irrespective of the electrode sizes. This paper reports detailed characteristic study of the most cost effective and accessible metal electrodes earth batteries. Operation of earth battery as a free electricity source was demonstrated successfully.
Content may be subject to copyright.
Second International Conference on Electrical Engineering
25-26 March 2008
University of Engineering and Technology, Lahore (Pakistan)
978-1-4244-2293-7/08/$25.00 ©2008 IEEE.
Experimental Study of Earth Batteries
N. Khan, Z. Saleem, N. Abas*
COMSATS Institute of Information Technology, H-8/1, Johr Campus Islamabad, Pakistan
*Department of Electrical Engineering, University of Gujrat, Gujrat, Pakistan.
nasrullahk@yahoo.com
Abstract: We report successful design, construction and operation of
an earth battery as an alternate energy source for low power electric
supply applications. Different combinations of metallic and non-
metallic solid, liquid and gas electrodes were investigated for
maximum potential difference. In view of robust and cost effective
use of this natural power technology by unskilled village consumers
most suitable combinations of the commonly available metals were
selected for further detailed characteristic studies. Combinations of
Magnesium anode and Coke cathode; Zinc anode and Graphite
cathode; Aluminum anode and Carbon cathode; Zinc anode and
Copper cathodes gave 2.05, 1.40, 1.10 and 0.9 volts per cell. Typical
rated power of a single Zn-Cu cell was measured to be few tens of
microamperes. Small power electronic devices such as calculators,
electronic watches, baby toys and cell phones and white light LEDs
were operated on site. The voltage level was found to increase
linearly by connecting multiple earth battery cells in series like
commercial lead acid battery. The load current was found to
increase by connecting earth cells in parallel. The source current
capacities were also found to increase by increasing surface areas of
the electrodes. However, single cell voltage was found to remain
constant irrespective of the electrode sizes. This paper reports
detailed characteristic study of the most cost effective and accessible
metal electrodes earth batteries. Operation of earth battery as a free
electricity source was demonstrated successfully.
I. INTRODUCTION
Reported free energy holy grails may include electrostatic
motors, geo-magnetic generators [1-2], air [3], sea [4] and
earth batteries [5-8]. Some free energy believers have often
been focusing on the perpetual motion machines using
scientifically unworkable ideas such as over unity devices,
millennium motors, resonance based self-charging and free
wheeling devices. There exists nothing as free energy source
such as mutual powering motor-generator set without any net
input or gravity based free running machines or negative
resistance based amplification. However, earth soil chemical
reactions and electron affinity based earth batteries may be
explored for low to high voltage DC potential to drive small
scale white emission LED lighting loads in remote hilly areas
or small scale electronic devices. They can also be considered
to replace high voltage low current charging power supplies
or ionization power supplies. Like earth batteries the sea
batteries also may be considered for similar applications.
However, air batteries can be used for bulk power production
and grid system operation [3]. In view of global energy crisis
to be caused by natural end of oil and gas within next 50 to
60 years time [9-11], it has become very important to look for
alternative energy sources to hold back the human race from
engagement to a great energy war [12-13].
Although, uranium [14] and coal [9] would continue to exist
for few centuries but they can not replace oil and gas despite
risks of radioactivity hazards (plutonium) and greenhouse
gases (CO2). Either, we can stop global warming at risk of
nuclear radiation or make the planet nuclear free at risk of
global warming due to increasing temperatures from1.4 to
5.8ºC from 1990 to 2100 by exponentially rising CO2
concentrations. Rise in earth surface temperature in past ten
hot years (1997-2007) was about 0.6ºC. Maximum
temperature has been recorded to be 52ºC in major cities of
Pakistan and 46ºC in Greece. Cool the home and heat the
planet or adapt to natural ways of life. We must stop use of
excessive energy for entertainment and retune ourselves to
new lifestyles requiring minimum amount of energy in the
form of cooling or heating. The scientists must work hard to
explore new sources of energy else be prepared to be
perished soon in a great energy war or global greenhouse
effect none knows which prevails earlier. This work is a
very honest effort to investigate the possibility of using
earth batteries for remote village lighting, communication
signaling and driving small scale electronic loads where
there is no alternate source of electricity or simple to
conserve electricity. Assuming uniform electrode profile the
potentials of some common metals electrode pairs in soils
are shown in Table 1. [15-17].
Table 1 Potential of Common Metals Suitable for Earth Battery
Anode materials
Cathode materials
Battery
Material
E (V)
Material
E (V)
Volts
magnesium
zinc
zinc
aluminium
iron
-1.75
-1.10
-1.10
-0.80
-0.50
coke
graphite
copper
carbon
coal
+0.30
+0.30
+0.20
+0.30
+0.30
2.05
1.40
0.90
1.10
0.80
To test the possibility of higher currents and voltage a few
large size C, Mg and Al electrodes are under construction or
testing. Unlike air batteries used in vehicles the earth
batteries have very low Wh capacities. It can not drive even
ordinary motorized baby toys. Above earth battery failed to
drive even an LED despite 0.7mA current due to low
voltage. It had an average 0.63 W power. It was still too
small to drive any motorized load except electronic digital
clock. A simple air battery may consist of aluminum foil (or
magnesium) and activated charcoal (or iron). Oxygen from
air may penetrate through saltwater soaked paper to react
with aluminum. Electrodes attached to aluminum and
carbon may produce enough useful voltage. Air battery cell
voltage depends upon reduction potential. Typical reduction
potentials of various materials at STP are shown in Table 2
[16-19]
Table 2 Standard Reduction Potentials of Elements at 25ºC
Per cell voltage ranges of air batteries are much lower than
air batteries. The best, Mg-C, earth battery has a maximum
2.05 volts whilst the best Li+(aq)-F2(g) air battery has 5.915
volts. However, air battery design needs to consider several
other economic aspects for commercial use. A common Zn-
Air battery can supply 312kWh in comparison with 22kWh
NiCd battery. Together they can power 200HP traction drive
at speed of 20mph or 35 mph using higher capacity batteries.
Recent trends are focused on increasing speed to 55mph to
cope with energy crisis. This technology is in use in several
countries since years. Air battery energy to weight and energy
to size ratios are 200-250Wh/kg and 300-375 Wh/L.
II. EXPERIMENTAL SETUP
An experimental study was conducted to measure exact
voltages and currents of an earth battery cells consisting of
zinc and copper electrodes. The electrodes arrangement on
earth’s surface in open air environment consists of simple
pricking of pointed electrodes on earth’s surface. The
electrode soil reaction voltage 0.92V may be used to drive
small scale lighting and electronic loads. Outside on bare
earth the currents and voltages were found higher at smaller
distances and lower at relatively larger distances between
cathode and anodes. The voltages and currents readings were
found unstable on the digital multi-meter. Repetition of above
experiment with interchange of electrodes from north to south
resulted in relatively increased voltages and currents.
Average magnitudes of voltages and currents were measured
to be 0.91±0.15V and 0.7±0.25mA for multiple electrodes.
Earth battery potential depends upon the electrode materials
and their standard reduction potentials. If we choose higher
positive and negative reduction materials the earth battery
voltage can be enhanced. Theoretical voltage of Zn-Cu earth
battery is 0.92V but our measurements conducted with UNI-
T professional digital VOAM # 1050444792 (Korea) were
about 0.90±0.25V. To construct a high voltage battery
suitable electrodes must be chosen. Common metals behave
similarly except current magnitude depends on electrode
surface areas. Variation of measured fluctuating voltages and
currents are shown in Fig.1.
Fig.1 Copper (south)-Zinc (north) earth battery voltages and
currents
When the same experiment was repeated inside lab using
insulated box mud cells the voltage and current was found
quite stable. It was supposed that the measurements made
outside on bare earth might have extra telluric earth currents
in addition to the normal earth battery currents. Further to
estimate the impact of telluric earth currents on the natural
directions on measured values of currents and voltages, the
zinc electrode was fixed in earth and copper electrode was
rotated for multiple directions from (north) to 90º (east)
to180º (south) and to 270º (west). The voltages and currents
at fixed radius of 9 feet circle were found to vary slightly
vary in magnitudes as shown in Fig.2.
Fig.2 Earth battery V/I characteristics for fixed zinc and
mobile copper electrode.
Electrode did not chemically corrode even after 8 to 9 hrs
continuous use. Stronger currents flow from south to north
and weaker currents from east to west. Currents were also
stronger for positive north and negative south electrodes.
Currents were found to flow from south to north. However,
it was not possible to connect earth battery cells in series to
increase the voltage as the electrodes from bottom become
short circuited through earth electrolyte materials.
Nevertheless, parallel connection of cells resulted in
increased currents due to increased surface areas. Spiral
design of electrodes due to large surface areas increases the
current magnitudes. Maximum magnitude of the measured
voltage was found to be 0.9 ±0.35 volts with currents in the
range of 3±0.25 A. When the same experiment was repeated
outside on open land the magnitude of current increased to
15±10 A. Both the current and magnitudes continued to
oscillate as if the some random potential source in addition to
normal soil reaction voltage was found modulating the
constant DC earth battery voltage.
III. SERIAL OPERATION OF EARTH BATTERIES
Due to short circuiting of electrodes the voltage can not
increase on bare earth surface. We need to isolate individual
cells to add up the voltage. To demonstrate serial addition of
voltages 13 DC battery cells were prepared in separate paper
boxes. The isolated earth battery cells were connected in
series to increase the voltage as shown in Fig. 3. The distance
between Zn and Cu electrodes in different cells varied from 8
to 10cm in Fig .3 (a) and 0.5 to 1cm in Fig.3 (b).
The voltage varied from 10 to 12V DC with low current but
still able to light up an LED. The mud resistance between the
electrodes was tens of M . To reduce the resistance a thin
film approach was applied by appending mud coatings on the
16 inch square I mm thick copper and zinc plates as shown in
Fig.4.
a. A twelve cells 10.30V/45mA earth battery
b. A four cells 2.43V/0.20mA earth battery
Fig.3. Experimental demonstration of serial connection of
earth batteries
Fig.4 Four inch square Zn/Cu plate electrodes 2.5V/30 A
earth battery
Four cells connected in series produced 2.5 to 3.25V DC
with 30 A current due to larger surface areas. It is to note
the voltage and current depend upon moisture content in dry
much. When it is complete dry the current reduces to zero
due to high resistance between electrodes. The reaction of
metal with soil requires moisture. Better if we go for mud
electrolyte instead of simple dry mud. The batteries
electrodes become partially rusted after long term operation.
A few results on rusting have already been published
elsewhere [20]. Further studies on large surface areas of
multiple electrodes are under investigation now.
IV. CONCLUSIONS
Results of experimental study on earth batteries using
copper and zinc electrodes are very encouraging. The initial
results for month operation of earth batteries has shown
reasonable potential for use in remote locations for
signaling as well as charging cell phone and white light
illumination applications. This interesting study was
undertaken as part of HEC funded research project on
Renewable Energy category. Being UET graduate (1984) I
feel a lot pleasure to present this research work through ICEE
2008 held in UET Lahore, Pakistan.
ACKNOWLEDGMENTS
This study was conducted as part of a Pakistan Higher
Education Commission funded renewable energy project no.
20-717: Minimum Ignition Study of Combustible Fuel Gases,
in the Department of Electrical Engineering, CIIT Johr
Campus Islamabad, Pakistan.
REFERENCES
[1] Gish, O. H., The Natural Electric Currents in the
Earth's Crust,” The Scientific Monthly, Vol. 32, pp.
5-2, 1989.
[1] G. M. Hopkins, Experimental Science:Elementary,
Practical and Experimental Physics. Munn & Co.,.
pp. 437 451, 1902.
[1] J. Cooper, Powering Future Vehicles with
Refuelable Zinc/Air Battery, Science &
Technology Review, pp. 6-13, October 1995.
[1] Lord Kelvin, Sea Battery: Method and Apparatus,
US Pat. No. 4153757, End of 1800s.
[1] Ryeczek, "U.S. Patent 4,457,988 Earth battery".
July 3, 1984.
[1] Daniel Drawbaugh, "U.S. Patent 211,322 Earth
battery for electric clocks". 1800s.
[1] M. Emme, "U.S. Patent 495,582 Ground generator
of electricity". 1900s.
[1] Dieckmann, George F., "U.S. Patent 329,724
Electric Earth Battery". November 3, 1885.
[1] K.S. Deffeyes, “Hubert’s Peak: The Impending
World Oil Shortage,” Princeton University Press.
2002: ISBN 0-691-09086-6.
[1] D. Goodstein,” Out of Gas: The End of the Age of
Oil. W. W. Norton’ Book 2005
ISBN 0-393-05857-3.
[1] H.H. Rogner,” An Assessment of World
Hydrocarbon Resources,” Annu. Rev. Energy
Environ, Vol. 22, pp. 217-262, 1997.
[1] M.C. Ruppert,” Crossing the Rubicon: The Decline
of the American Empire at the End of the Age of
Oil, New Society. 2005: ISBN-13: 978-
0865715400.
[1] L.C. Kleveman,” The New Great Game: Blood and
Oil in Central Asia,” Atlantic Monthly Press. 2004:
ISBN 0-87113-906-5.
[1] K.S. Deffeyes, I.D. MacGregor, “ World Uranium
Resources, Scientific America,” Vol. 242, pp. 66-67.
1980.
[1] http://en.wikipedia.org/wiki/Earth_battery
[1] James Napier, “A manual of electro-metallurgy,” pp.
48-49, 1876
[1] A. A. Fesquet, Oliver Byrne, and John Percy,
The Practical Metal-worker's Assistant. H.C. Baird
& Co., pp. 529-530, 1878.
[1] E. Katz, "Alexander Bain". The history of
electrochemistry, electricity and electronics;
Biosensors & Bioelectronics.
[1] R. J. Edward,” Measurement of Soil Resistivity &
Calculation of Earth Electrode Resistance. 15th
February 1998.
[1] N. Khan, N. Mariun, Z. Saleem, N. Abas, Fossil
Fuels, New Energy Sources, and the Great Energy
Crisis, Renewable & Sustainable Energy
Reviews, Online: December 2007.
... The energy can reduce their dependence on primary energy. However, earth soil chemical reactions and electron affinity based earth batteries may be explored for low to high voltage DC potential to drive small scale white emission LED lighting loads in remote hilly areas or small scale electronic devices [2]. They can also be considered to replace high voltage low current charging power supplies or ionization power supplies [3][4]. ...
... However, the problems encountered in the production of electricity from the soil [2] are a small charge of electricity which needs to increase the power of the original. This study is use soil to produce electric current to produce of soil. ...
... It cans charge from soil are shown in Table 1. [2] The material with higher capacity can absorb more tightly to the pole. Therefore, the nutrient management of plant, soil is not only. ...
Conference Paper
Full-text available
Currently, the demand for energy is increasing. We are the focus renewable energy source, as Lopburi, Thailand because Lopburi has a lot of marl soil. This project study about potential of marl soil to produce electricity by using different pool rod the cathode (+) and anode (-) into marl. It’s may affect the oxidation reaction at the cathode, and reduction of the anode cause voltage. The experiment results were mixed vinegar with marl, using copper and zinc rods show the best result, which the voltage is 1.09-V/cell, when pH was decreased temperature increased. When tested with the result current up to 3 mA/cell. The phone battery charging is 12.72 V, 140.8 mA in 4.5 hours. A mineral marl soil test, after test found that Ferric, Potassium, Aluminum and Silica were gone. Thus, the result shown that the electricity that produce form marl soil can be use with low power load such as LED load, phone battery charging etc.
... That is an instantaneous power of 0.41 mW when separated at a distance of 250 inches. At a distance of 10 inches this current is about 0.6 mA which increases the instantaneous power to 0.54 mW [21]. Throughout the process it is noted that the potential remains constant while the current decreases. ...
... 7,10 For all these reasons, a change of energy transition for electrical power is crucial from non-renewable origins to renewable sources as renewable technology promises to reduce CO 2 emission in the atmosphere and provide environmentally friendly electricity. [11][12][13][14][15][16][17][18][19][20] Moreover, use of renewable energy sources, in particular solar energy, can minimize electricity supply and demand problems in many developing countries such as in Pakistan. According to IEA, renewable energy will meet almost 30% of electricity demands becoming world's second largest power generation source by the year 2035. ...
Article
Full-text available
To meet heating demand without global warming is a huge target for the energy community these days. To attain this challenge, solar energy harvesting to meet domestic hot water demand is a promising solution. Carbon dioxide(CO2) is becoming ever more significant as heat transporting fluid. Simulation based efficiency assessment models are requisite for analogous advances. This research presents a dynamic simulation model of high temperature concentrated solar plant using directly heated molten salt to indirectly power a supercritical CO2 Brayton cycle. Target of the study is toachieve 1 MW generation and simulation work is performed in TRNSYS computer software. The operating conditions for the plant cycle and efficiency for indirectly heated CO2 recompression Brayton cycle are also calculated with the help of Engineering Equation Solver (EES). The system is divided into three major loops: solar thermal heat collection, Power generation, and heat recovery. Results have shown overall cycle efficiency up to 40%. During the day hours from 4688‐4697, receiver provides a constant outlet temperature of 700°C with a fluid inlet flow rate of 15 kg/sec and mediating fluid after exchanging heat enters the receiver's end at 524°C. An optimized value of 2.9 is selected as pressure ratio to meet supercritical conditions at the compressor inlet. Output power generated is 3.035 MW with turbine efficiency is 92%. The power calculated for main compressor and re‐compressor are 0.68 MW and 0.228 MW respectively. This article is protected by copyright. All rights reserved.
... Multimeter is used for measure voltage between two electrodes. To series multiple electrode for increase the voltage, vermicompost cell must be isolated individually because it cannot immersed in same container due to short circuit [10]. ...
Article
Full-text available
Wastages such as grated coconut meat, spent tea and used sugarcane had contributed negative impacts to the environment. Vermicomposting method is fully utilized to manage the wastes towards a more sustainable approach. The worms that are used in the vermicomposting are Eisenia foetida and Eudrillus euginae. This research shows that the vermicompost of wastages has voltage of electrical energy and is able to light up the Light-Emitting Diode (LED) device. Based on the experiment, the use of replicated and double compartments of the component will produce double of voltage. Hence, for conclusion, this harmless and low cost technology of vermicompost can act as a dry cell in order to reduce the usage of hazardous chemicals that can contaminate the environment.
Article
Full-text available
Hydropower dams on rivers in the Indus Basin are becoming new elements in power geopolitics due to the threat of “aqua bombs” to downstream regions. Water law may limit such perceived water wars. The transboundary river water sharing agreements that bind bordering states are overstretched, particularly between Pakistan and India. Meanwhile, factors such as the expansion in industry and population, global warming, and reduction in oil and gas resources diminish scarce natural water resources. In addition, due to water pumping at levels above natural recharge rates, the underground water table has reached a state of continual free fall in the Indian and Pakistani Punjab. This work points out the dire need to reform international law to address such transboundary river conflicts, as water conflicts may become fully fledged armed conflicts with the current approach. The concurrence of power, energy, food, and water crises may wreak havoc on international river agreements if not addressed in international law. However, the laws that define rights among developed states may not be suitable for developing countries, and water and food security are critical issues for sovereign nations. Water sustains life, effectively determining all other geopolitical issues. The aim of this work is to investigate how international law could be adjusted with regard to international water sharing in order to resolve issues such as the energy crisis, economic collapse, global warming, and climate change.
Article
The usage of chemical battery is very critical nowadays because of their hazardous chemical contains that can cause pollution and need to dispose properly in order to avoid pollution towards the eco-system. Hence, the earth battery is an erstwhile concept designed to generate electricity by using two dissimilar electrodes buried in the ground or immersed in the sea. Although it has been proven to generate electricity, the voltage produced is quite low while the voltage intensity could not be sustained for a long period of time. This paper attempts to explore the potential of using organic wastes as additives in the soil of ground-based earth batteries to improve its performance. Three types of organic wastes were studied; Palm Oil Mill Effluent (POME), pineapple waste and lemon waste. Each organic waste is added into separate damped clay soil containers with a ratio of 20:80. Then a copper and an iron electrode are partially buried inside the soil and the electrical properties are measured by connecting a multimeter at the electrodes. The result shows that there is marginal improvement for all three organic wastes in terms of voltage compared to damped clay soil alone. The results also show that the voltage output of these samples could be sustained for seven days.
Article
Full-text available
Abstract Assessments of global coal, oil, and natural gas occurrences usually focus on conventional hydrocarbon reserves, i.e. those occurrences that can be exploited with current technology and present market conditions. The focus on reserves seriously underestimates long-term global hydrocarbon availability. Greenhouse gas emissions based on these estimates may convey the message that the world is running out of fossil fuels, and as a result, emissions would be reduced automatically. If the vast unconventional hydrocarbon occurrences are included in the resource estimates and historically observed rates of technology change are applied to their mobilization, the potential accessibility of fossil sources increases dramatically with long-term production costs that are not significantly higher than present market prices. Although the geographical hydrocarbon resource distribution varies significantly, a regional breakdown for 11 world regions indicates that neither hydrocarbon resource availability nor costs are likely to become forces that automatically would help wean the global energy system from the use of fossil fuel during the next century.
Article
Crustal-distribution and the mining-history models can be used to estimate world resources. The diverse deposits combine to form a simple log-normal curve, the smoothly ascending slope of which indicates approximately a 300-fold increase in the amount of uranium recoverable for each 10-fold decrease in ore grade. The five most important categories of deposits in descending order of content are 1) vein; 2) uncomformity, 3) sandstones-caliche; 4) fossil placers 5) phosphates-black shales. Sandstone has dominated U.S. production. Deposits of lower grades are not yet economic unless a valuable by-product can also be extracted. Examples are some of the gold and phosphate mines. There should be ample for an expanding nuclear-power industry. If estimates of resources and the prospects of more efficient reactors turn out to be correct, the fast breeder reactor could be postponed for two decades. -Forrest McElhoe Jr.
Book
The world will start to run out of cheap, conventionally produced oil much sooner than most people expect, possibly within this decade. This talk will discuss the reasoning that leads to that conclusion and the likely consequences if it is correct. It may be possible, with considerable difficulty to substitute other fossil fuels for the missing oil, but if we do that we may do irreparable damage to Earth's climate. And even then we would start to run out of all fossil fuels, including coal, probably within this century. Can civilization survive if that happens? We will consider the possibilities.
Book
Global oil production will probably reach a peak sometime during this decade. After the peak, the world's production of crude oil will fall, never to rise again. The world will not run out of energy, but developing alternative energy sources on a large scale will take at least 10 years. The slowdown in oil production may already be beginning; the current price fluctuations for crude oil and natural gas may be the preamble to a major crisis. In 1956, the geologist M. King Hubbert predicted that U.S. oil production would peak in the early 1970s.1 Almost everyone, inside and outside the oil industry, rejected Hubbert's analysis. The controversy raged until 1970, when the U.S. production of crude oil started to fall. Hubbert was right. Around 1995, several analysts began applying Hubbert's method to world oil production, and most of them estimate that the peak year for world oil will be between 2004 and 2008. These analyses were reported in some of the most widely circulated sources: Nature, Science, and Scientific American.2 None of our political leaders seem to be paying attention. If the predictions are correct, there will be enormous effects on the world economy. Even the poorest nations need fuel to run irrigation pumps. The industrialized nations will be bidding against one another for the dwindling oil supply. The good news is that we will put less carbon dioxide into the atmosphere. The bad news is that my pickup truck has a 25-gallon tank.
Method and Apparatus, US Pat. No. 4153757, End of 1800s
  • Lord Kelvin
  • Sea
  • Battery
Lord Kelvin, Sea Battery: Method and Apparatus, US Pat. No. 4153757, End of 1800s.
A manual of electro-metallurgy
  • James Napier
James Napier, "A manual of electro-metallurgy," pp. 48-49, 1876
Experimental Science:Elementary, Practical and Experimental Physics
  • G M Hopkins
G. M. Hopkins, "Experimental Science:Elementary, Practical and Experimental Physics. Munn & Co.,. pp. 437 -451, 1902.