62 Mr. A. R. McLeod on the 



■in bore in the case o£ mercury, the lags for mercury are 

 given by the expressions (43) and (44), while the lags for 

 alcohol have the values 



Mfft+sk) ^ 



for the sphere of radius c ; and 



g KA + m)- • • • • • c«) 



for the cylinder of radius c. 



But for mercury we may neglect the first terms in (43) 

 :and (44), and so these lags become 



For the mercury sphere Gpcrcjubi/^h, . . (47) 

 „ „ „ cylinder -^-\f j • • - (48) 



Messrs. Pastorelli & Rapkin of Hatton Garden state that 

 fine capillary tubes, when used with alcohol, must have a 

 circular section as otherwise the meniscus is distorted. 

 The limiting diameter of capillary which may be used they 

 give as *25 mm., while *50 mm. would be a good working- 

 limit. Mercury thermometers, on the other hand, can ap- 

 parently be made with the finest capillary tubes that can be 

 drawn. Two samples of ordinary small clinical thermo- 

 meters, supplied by Messrs. Pastorelli & Rapkin, were 

 broken across half-way up the stem, and the capillary tube 

 was measured under the microscope. In one the elliptical 

 tube had dimensions *10 mm. X '031 mm. with a sectional 

 area of *0025 sq. mm. In the other, the dimensions were 

 •063 mm. and *043 mm. and the area was *0021 sq. mm. 



James J. Hicks of Hatton Garden supplied samples of 

 .alcohol and mercury thermometer tubes having a glass wall 

 of irregular thickness, suitable for magnifying the diameter 

 of the capillary tube and so enabling readings to be taken at 

 a distance. The alcohol tube had a circular bore of 1*0, mm. 

 diameter and is used in the Strutt Thermometers supplied 

 to the R.A.F. The mercury tube had a circular bore of 

 '125 mm. diameter. This was stated to be the smallest 

 practicable mercurial bore (presumably with this type of 

 magnifying stem). The ratio of the sections of these 

 specimens is 64 : 1. 



Taking *002 sq. mm. as the smallest section of capillary 



