of Edinhurgh, Session 1882-83. 
25 
according to the method described by Professor Tait in a letter read 
by Sir William Thomson at the Southampton meeting of the British 
Association (see Nature, vol. xxvi. p. 639, 1882). They consist 
of two series — the first, a series of rough experiments made, first, to 
determine whether or not the method would work, and, secondly, to 
find the dimensions of the apparatus which would give the best 
result ; the second, a series of more careful experiments made when 
the method was found to give satisfactory results. 
