10 



Messrs. Thorpe and Biicker's Remarks on 



is enlarged by outward pressure due to that cause, and the zero 

 descends. If the above view be correct, it would follow that 

 a thermometer open to the air and kept always in a vertical 

 position would always exhibit a descending zero; the descent 

 in the first stage being due to expansion and set as before, but 

 in the later stages simply to the weight of the mercury acting 

 upon a bulb now rendered partially plastic by heat. I cannot 

 find that other investigators have left any record of such an 

 experiment." Dr. Mills then gives the following table to 

 show that the zero of an open thermometer observed after 

 heatings to 50°, 100°, 150°, and so on up to 350°, fell more 

 and more after each heating : — - 



Zero (therm. 20). 



Scale. 



Depression. 



Before experiment . . . 

 After 50° 



+ •262 C. 



•134 

 -•058 



•203 



•360 



•547 



•494 



•570 



o-ooo 



•128 

 •320 

 •465 

 •622 

 •809 

 •756 

 •832 



„ 102 



„ 150 



„ 200 



„ 250 



„ 310 



„ 350 





" The first seven observations were made consecutively on 

 one day, the eighth nearly two days later. The temperatures 

 are not corrected." 



We may point out that observations 6 and 8 in the above 

 table are discordant, and that, if we have to reject one, it 

 should rather be the eighth, which was made two days after 

 the others, than the sixth, which is more directly comparable 

 with them. If we therefore reject the last experiment instead 

 of the sixth, as Dr. Mills practically does, the table is in con- 

 tradiction to his theory, and shows a maximum depression 

 after the thermometer was heated to 250°. 



In any case, as the increments of the depressions at higher 

 temperatures are less than for the lower, we think Dr. Mills 

 ought to have tried whether, if these results were expressed 

 by a formula similar to that employed in the preceding cases, 

 it would not have given a minimum at some higher tempera- 

 ture. The fact that it is impossible to carry on the experi- 

 riments much above 350° with mercury is no reason for 

 regarding the formulas as less trustworthy beyond that point 

 than the others which were treated in this way. 



If by a rising zero is meant a zero which is less depressed after 

 every heating, some observations of our own prove that it is 

 quite possible to obtain this with an open tube. The bulb of a 

 Jolly's air-thermometer of about 90 cub. centim. capacity, 



