388 Dr. G. Johnstone Stoney on the 



atmospheric temperatures and pressures is somewhere about a 

 unit-eighteen (10 1S ). Hence the number of molecules in a 

 litre will be about a unit-XXIV. Now, a litre of hydrogen 

 at atmospheric pressures and temperatures weighs, roughly 

 speaking, a decigramme. Hence the mass of each molecule 

 of hydrogen is a quantity of the same order as a decigramme 

 divided by a unit-XXIV, i. e. a XXVth gramme. The che- 

 mical atom is half of this. Hence the mass of a chemical 

 atom of hydrogen may be taken to be somewhere about half a 

 twenty-fifth-gramme. There is no advantage in retaining the 

 coefficient half in an estimate in which we are not even sure 

 that we have assigned the correct power of 10 ; and I will 

 therefore, for the sake of simplicity, take the XXVth gramme 

 as being such an approach as we can attempt to the value of 

 the mass of an atom of hydrogen. 



10. Now, it has been ascertained by experiment that, for 

 every ampere of electricity that passes, ninety-two sixth- 

 grammes (i. e. ninety-two millionths of a gramme of water) are 

 decomposed (see Brit.-Assoc. Report, 1863, p. 160). This 

 w-ater is the result of a secondary action in the voltameter ; 

 but that does not affect the present inquiry. Ninety-two Vlth 

 grammes of water contain about one Vth gramme of hydrogen, 

 w r hich is therefore the quantity evolved. The metric unit of 

 electricity e x is 100 amperes, and will therefore set free 100 

 Vth grammes of hydrogen, i. e. one milligramme. Now it 

 appears, from the last paragraph, that this quantity of hydro- 

 gen contains ^ atoms, i. e. XXII atoms. And as there is a 

 bond ruptured for each atom of hydrogen set free, this is also 

 the number of bonds broken ; in other words, the quantity of 

 electricity corresponding to each chemical bond separated is 



Ei= xxri ei ( 3 ) 



Collecting our numerical results, they are 



Y 1 = 3 VIII metres per second, . . (1) 



G- 2 A_ (2 \ 



^ 1 ~3X11F ^ l) 



El= XXlT ( 3 ) 



1 

 = == ampere. 



We have thus obtained approximate values in known mea- 

 sures for the three great fundamental units offered to us by 

 Nature, upon which may be built an entire series of physical 



