402 Prof. S. U. Pickering on 



capillarity of the tubes acting on the expansibility of the 

 bulbs, and not to the action of the bulbs only, and thus the 

 differences observed between the behaviour of the two instru- 

 ments might easily be accounted for by slight differences in 

 the shape or size of the bore at various points. In order to 

 test the validity of such an explanation, which at first sight 

 appeared highly probable, other experiments were performed 

 with these instruments, taking care to make all the obser- 

 vations at exactly the same temperature, removing some of 

 the mercury into the upper chamber, so as to make the 

 different points on the scale correspond to the same Cen- 

 tigrade temperature. The somewhat bulky details of the 

 experiments may here be omitted, and the general results 

 only given. Table I. contains these results; those which were 

 obtained originally, and have been given in the previous 



Table I. 



Thermometer No. '39. 

 Scale-Beading 465 457* 270* 162 142* mm. 



D »^ea^ g } 0-5 -46, -27* 17 -16™*, 



Relative capacity of 1 



tube at the point L 46*1 461 45 45*6 45'6 



taken J 



Thermometer No. '616. 



Scale-Eeading 562 458 458* 289 154 142 140* mm. 



M IZS„ g in r ead!n g n s g } «•« * <*• -78 -67 -62 -91, nun. 

 Eelative capacity of 1 



tube at the point I 40-3 40 40 39'3 401 401 401 



taken J 



communication, are marked by an asterisk; and any small 

 discrepancies observed between them and the fresh experi- 

 ments may be attributed to differences in the actual tempera- 

 ture of the observations, the recent experiments only being 

 strictly comparable with each other, having all been performed 

 at 10 o, 5 C. The readings and the differences are expressed here 

 in mm. of the column, instead of cm. (or scale-degrees) as in 

 the former communication. 



To whichever thermometer we confine our attention, it is 

 perfectly obvious that the magnitude of the differences bears 

 no relation to the size of the bore. Taking the original 

 experiments with '39, the difference as judged by the size of 

 the bore should be least at 457, and greatest at 270, and of 

 intermediate value at 142 mm.; whereas they are found to 

 be greatest at 457 and least at 142 mm. Again, with 

 No. '616, the differences should be greatest at 289, and least 

 at 562 mm.; whereas they are practically equal at these two 

 points, and greater (taking the later experiments only) than 



