360 HENKY A. EOWLAND 



So effective was this arrangement that, although some of the ther- 

 mometers read to 0-007 C., yet they would remain perfectly stationary 

 for several minutes, even when at 40 C. At very high temperatures, 

 such as 80 or 90 C., the burner was kept under the vessel w all the 

 time, and supplied the loss of the outer vessel by radiation. The inner 

 vessel would under these circumstances remain at a very constant tem- 

 perature. The water in the outer vessel never differed by more than 

 a small fraction of a degree from that in the inner one. 



To get the and 100 points the upper parts of the vessel above 

 the line a & were removed, and ice placed around the bulb of the air 

 thermometer, and left for several hours, until no further lowering took 

 place. For the 100 point the copper vessel shown in Fig. 3 was used. 

 The portion y of this vessel fitted directly over the bulb of the air 

 thermometer. On boiling water in x, the steam passed through the 

 tube to the air thermometer. It is with considerable difficulty that 

 the 100 point is accurately reached, and, unless care be taken, the 

 bulb will be at a slightly lower temperature. Not only must the bulb be 

 in the steam, but the walls of the cavity must also be at 100. To 

 accomplish this in this case, a large mass of cloth was heaped over the 

 instrument, and then the water in x vigorously boiled for an hour or so. 

 After fifteen minutes there was generally no perceptible increase of 

 temperature, though an hour was allowed so as to make certain. 



The external appearance of the apparatus is seen in Fig. 2. The 

 method of measuring the pressure was in some respects similar to that 

 used in the air thermometer of Jolly, except that the reading was taken 

 by a cathetometer rather than by a scale on a mirror. The capillary 

 stem of the air thermometer leaves the water vessel at a, and passes 

 to the tube &, which is joined to the three-way cock c. The lower part 

 of the cock is joined by a rubber tube to another glass tube at d, which 

 can be raised and lowered to any extent, and has also a fine adjustment. 

 These tubes were about 1-5 cm. diameter on the inside, so that there 

 should be little or no error from capillarity. Both tubes were exactly 

 of the same size, and for a similar reason. 



The three-way cock is used to fill the apparatus with dry air, and 

 also to determine the capacity of the tube above a given mark. In 

 filling the bulb, the air was pumped out about twenty times, and 

 allowed to enter through tubes containing chloride of calcium, sulphuric 

 acid, and caustic soda, so as to absorb the water and the carbonic acid. 



