280 



Wadsworth — Determination of Specific 



hooks to a light brass ring, which in turn is pivoted in the 

 forked end of a long wooden lever a, o, c. This lever is hung 

 on a link at o and has a pin at c which moves in a slot cut in a 

 plate of brass or hard wood of such shape that a moves up 



and down in a straight line. The end c is so weighted as to 

 slightly overbalance the ring, bracket, etc., hung on the other 

 end. The thermometer, t, is read by means of a very short 

 focus telescope, made by slipping over the end of an ordinary 

 reading telescope, a cap carrying a second object glass of about 

 the same focal length as that of the telescope. It is balanced 

 on pivots, d, so as to easily follow the movement of the mercury 

 column. The inner calorimeter, which is filled with water 

 almost up to the neck, is completely enclosed in a water jacket 

 whose inner walls are blackened (not left bright as usual). The 

 cover is double, of heavy sheet metal, and the hole in the 

 center through which the body drops into the inner calori- 

 meter has a hinged trap door, f which can be turned back 

 against a step on the calorimeter cover. When a good water 

 supply is available, I have found that the temperature of this 

 water jacket is most easily kept constant by allowing a slow 

 constant stream to flow through it from bottom to top, from a 

 large tank supplied from the city (or building) mains. 



The method of introducing the hot body into the calori- 

 meter is almost self-explanatory from what has preceded. The 

 observer at the eye end of the telescope pulls open by aid 

 of a string the trap door in the top of the water jacket, and 

 then by means of a second string pulls down the end of the 

 wire, ac (fig. 2), releasing the car and the door, _B, at the 

 same instant. The car runs rapidly down the track, throwing 

 aside in its course the flaps of woolen cloth which cover the 

 openings in the interposed wooden screens (see fig. 2), and is 

 brought to rest by a rubber buffer which stops it in such a 



