160 REPORT—1863. 
British System.—Relation between Absolute and other Units. 
One absolute unit of { ms = 0:0310666 ae grain } in London. 
fo) 
force. 
work. 
In London { — of a grain _ 39.1889 absolute units of { 
fo} 
force _1 f{ unit weight 
work“ g | unit weight x unit length 
g in British system =32-088 (1+ 0-005133 sin? \), where A=the latitude of 
the place at which the observation is made. 
Heat.—The unit of heat is the quantity required to raise the temperature of 
one grain of water at its maximum density 1° Fahrenheit. 
Absolute mechanical equivalent of unit of heat=24861=772 foot-grains 
at Manchester. 
Thermal equivalent of an absolute unit of work =0-000040224., 
Thermal equivalent of a foot-grain at Manchester =0°0012953, 
Electrochemical equivalent of water =0-02, nearly. 
One absolute unit of { } everywhere. 
Metrical System.—Relation between Absolute and other Units, 
One absoliite unit bf { force _ y.ogogsa1 Weight of a gramme } bit Paris, 
work metre-gramme 
{ force. 
At Pach { the weight of a gramme _.gog¢g absolute units of oe 
or metre-gramme 
: force _1 unit weight 
One absolute unit of { Ears. re ann wien Esc ante lanestle } everywhere, 
g in metrical system = 9-78024 (1+ 0-005133 sin’ d), where \ =the latitude 
of the place where the experiment is made. 
Heat.—The unit of heat is the quantity required to raise one gramme of 
water at its maximum density 1° Centigrade. 
Absolute mechanical equivalent of the unit of heat=4157-25=423-542 
metre-grammes at Manchester. 
Thermal equivalent of an absolute unit of work =0-00024054. 
Thermal equivalent of a metre-gramme at Manchester=0-00236154. 
Electrochemical equivalent of water =0-0092, nearly. 
56. Note to the Table of Dimensions, by Professor Clerk Maxwell.—All the 
measurements of which we have hitherto treated are supposed to be made in 
the same medium—ordinary air; but Faraday has shown that other media 
have different properties. Paramagnetic bodies, such as oxygen and salts of 
iron, when placed in media less paramagnetic than themselves, behave as 
paramagnetic bodies; but when placed in media more paramagnetic than 
themselves, they behave as diamagnetic bodies. 
Hence magnetic phenomena are influenced by the nature of the medium in 
which the bodies are placed, and the system of units and of measurements 
which we adopt depends on the nature of the medium in which our experi- 
ments are made. If we made our experiments in highly condensed oxygen, 
magnets would attract each other less, and currents would attract each other 
more, than they do in common air; and the reverse would be the case if we 
worked in a sea of melted bismuth. 
Now if we take into account the “ coefficient of magnetic induction ” of the 
medium in which we work, and instead of assuming that of common air to be 
unity, assume it proportional to the density of that part of the medium to 
