390 HENKY A. EOWLAXD 



cific heat of water is about constant on the mercurial thermometer made 

 by Baudin, but decreases to a minimum at about 30 when the reduction 

 is made to the air thermometer or the absolute scale, or, indeed, the Kew 

 standard. 



As this curious and interesting result depends upon the accurate 

 comparison of the mercurial with the air thermometer, I have spent 

 the greater part of a year in the study of the comparison, but have not 

 been able to find any error, and am now thoroughly convinced of the 

 truth of this decrease of the specific heat. But to make certain, I have 

 instituted the following independent series of investigations on the 

 specific heat of water, using, however, the same thermometers. 



The apparatus is shown in Fig. 4. A copper vessel, A, about 20 cm. 

 in diameter and 23 cm. high, rests upon a tripod. In its interior is a 

 three-way stopcock, communicating with the small interior vessel B, 

 the vessel A, and the vulcanite spout C. By turning it, the vessel B 

 could be filled with water, and its temperature measured by the ther- 

 mometer D, after which it could be delivered through the spout into 

 the calorimeter. As the vessel B, the stopcock, and most of the spout, 

 were within the vessel A, and thus surrounded by water, and as the 

 vulcanite tube was very thin, the water could be delivered into the 

 calorimeter without appreciable change of temperature. The proof of 

 this will follow later. 



The calorimeter, E, was of very thin copper, nickel-plated very 

 thinly. A hole in the back at F allowed the delivery spout to enter, 

 and two openings on top admitted the thermometers. A wire attached 

 to a stirrer also passed through the top. The calorimeter had a capac- 

 ity of about three litres, and weighed complete about 388-3 grammes. 

 Its calorific capacity was estimated at 35-4 grammes. It rested on 

 three vulcanite pieces, to prevent conduction to the jacket. Around 

 the calorimeter on all sides was a water-jacket, nickel-plated on its 

 interior, to make the radiation perfectly definite. 



The calorific capacity of the thermometers, including the immersed 

 stem and the mercury of the bulb, was estimated as follows : 14 cm. of 

 stem weighed about 3-8 gr., and had a capacity of -8 gr.; 10 gr. of 

 mercury had a capacity of -3 gr.; total, 1-1 gr. 



Often the vessel B was removed, and the water allowed to flow 

 directly into the calorimeter. 



The following is the process followed during one experiment at low 

 temperatures. The vessel A was filled with clean broken ice, the open- 

 ing into the stopcock being covered with fine gauze to prevent any 



