354 THIRD REPORT 1833. 



tigrade *) causing at high temperatures the volume of the water 

 to vary more than the pressure of 3, 4, or even 5 atmospheres. 



"The improved apparatus is represented in the diagram fig. 1. 

 Its principal parts are the same as in the earlier; in each of them, 

 however, some change is introduced. A B C D is a strong 

 glass cylinder, having at the top a cylinder E F G H, contain- 

 ing a piston I m n o, moved by a screw K K, as in the first 

 apparatus ; but the handle 1 1 is now arranged in such a man- 

 ner that the screw can be turned without interruption ; by this 

 means the effect is accelerated, and subitaneous strokes avoided. 

 The bottle c c c, with its capillary tube a a, is different from 

 the earlier only so far, that the tube is not soldered to the bot- 

 tle, but merely adjusted by grinding. This alteration is not 

 necessary except when solid bodies are to be compressed. The 

 scale efg h is divided into parts of Vu inch. In order to ex- 

 clude the water with which the large cylinder is filled, from com- 

 munication with that of the bottle, the top of the tube a a is 

 covered with a small diving-bell, or rather diving-cap, ppp, 

 whose conical shape has the advantage of preventing the water 

 from reaching the top of the tube a a, even when the air is com- 

 pressed to a tenth or twelfth part of its first volume. Its margin 

 is loaded with a ring of lead or brass, c di& a. glass tube with 

 proper divisions, containing air, whose compression measures 

 the pressure ; its inferior part is loaded with some lead or a 

 ring of brass. ^ m s is a siphon ; P, a vessel containing water ; 

 i i are two buoys of cork for lifting up the bottle and the glass 

 tube cd; s r is a tube of brass, which can be stopped by a 

 screw. In the beginning and at the conclusion of the experi^ 

 ment it serves to introduce water into the space E F G H, or to 

 get it out again. Before the experiments the calibre of the 

 two tubes must be exactly ascertained, and the relative capaci- 

 ties of the bottle and its capillary tube determined by the quan- 

 tities of mercury they can admit. I have had some tubes in 

 which -^ of an inch (making one division) held only 2 mil- 

 lionths of the capacity of the bottle, in others they have held 

 more, in some even as much as 7 millionths. The capacity of 

 the bottle was not less than 1^ pound, often 2 pounds of mer- 

 cury. It is next filled with water, which must be boiled in the 

 bottle in order to expel the air, which might be suspected of 

 having a great influence in these experiments, though Canton 



* The unit of thermical measurement is the distance between the freezing 

 and the boiling point. I think that the most natural expression for the tem- 

 peratures would be this unit and its fractions. Thus, the temperature 0'50 

 would be the same as 50° centigrade, 19-30 the same as 1930° centigrade. 

 T will mark this metrical measure by Th. If this innovation should not please, 

 I wish that it might be suppressed, and centigrade degrees put in the place, 

 which is an easy change. 



