48 Mr. E. H. Griffiths on the Influence of 



the method (such as doubts as to the actual resistance of the 

 conductor when its temperature is raised by the current, 

 &c), but when once these difficulties are overcome, there is 

 no such accurate means of determining the quantity of heat 

 passed into a calorimeter in a given time. 



The limits of this paper forbid any detailed account of the 

 somewhat complicated apparatus used in this investigation, and 

 I do not contend that it is of the form which I should have 

 selected had my object simply been to determine the specific 

 heat of aniline. I am at present engaged in a determination 

 of the latent heat of evaporation of water and other liquids at 

 different temperatures, consequently the apparatus has been 

 designed and put together in anticipation only of that investi- 

 gation, and many portions of it are unnecessary and in fact 

 detrimental to the inquiry I am now describing. Hence I 

 have been compelled to adopt methods of observation which 

 may not, at first sight, seem the most advantageous. 



I have in my possession an apparatus for maintaining the 

 walls of a chamber at a constant temperature. The arrange- 

 ment has been fully described in a communication entitled "The 

 Mechanical Equivalentof Heat," Phil. Trans. clxxxiv. A (1893), 

 and as I shall somewhat frequently have to refer to this paper, 

 I will now label it with the letter " J." Briefly, the apparatus 

 as there described consists of a tank containing about 20 

 gallons of water within which is a steel chamber shaped some- 

 what like a hat-box with vertical sides, the space between the 

 double walls and Moor containing rather more than 70 lbs. of 

 mercury, which communicates by a narrow tube with a gas- 

 regulator differing but little from the ordinary pattern. Thus 

 a row of about 50 tiny gas-jets (placed under a tube through 

 which water is always flowing) are so controlled -as to be dis- 

 tinctly affected by a change of 4<jo° C. in the temperature of 

 the steel chamber. An addition has been made to the appa- 

 ratus since the publication of the description in paper J, where 

 it is stated that tap-water continually passed into the tank 

 through a silver tube placed above the gas-jets : this plan 

 answered admirably from the temperature of the tap-water 

 (10° to 12° C.) to about 30° C. Last year, however, Prof. Cal- 

 lendar and I wished to use the tank for purposes of comparison 

 of platinum and air thermometers up to 50° or 60 c C, when 

 it was found that alterations in temperature presented them- 

 selves, occasionally amounting to as much as -^q C, — the lag 

 in the temperature of the large mass of mercury being so 

 great that when the gas was lowered by the action of the 

 regulator, the resulting inflow of cold water tended to lower 

 the temperature of the tank before the reaction of the regu- 



