18 Prof. W. H. Bragg on the " Elastic Medium " 



possible. To accomplish this, a platinum capillary tube is to 

 be cemented into the stem of the porcelain air-thermometer, 

 by bringing atmospheric pressure to bear on the outside of the 

 exhausted bulb, while the neck is being heated on the 

 revolving table by the oxyhydrogen blowpipe, to the point of 

 sufficiently reduced viscosity for adhesion. Experiment must 

 show whether the bulb of the type figure 2 will ultimately 

 answer all requirements, or whether a bulb which combines 

 the features of figs. 2 and 3 will be necessary. Note that an 

 independent method of standardization of the non-inglazed 

 reentrant porcelain air-thermometer bulb, by thermal com- 

 parison with a reentrant glass air-thermometer bulb, of known 

 constants, is also feasible. Such a comparison is to be made 

 above 200°, to obviate all moisture and condensation errors, 

 and either directly, in the elliptical revolving muffle (§ 9) , or 

 indirectly, through the intervention of the same thermocouple. 

 I have constructed vapour baths (naphthalene, diphenyla- 

 mine) for this purpose. 



I may add, in passing, that during my experiments with 

 molten rock I was surprised by the tenacity with which the 

 basic magma adheres to platinum and protects it. A platinum 

 bulb covered with some refractory glazing may therefore be 

 looked to, when temperatures beyond the reach of the porce- 

 lain bulb (say about 1400°) are to be measured. I believe, 

 however, that for the case of platinum apparatus, the method 

 of absolute air-thermometry based on the high temperature 

 viscosity of gases is more promising, if only some mathe- 

 matical physicist would give us an expression for the depend- 

 ence of gaseous viscosity on temperature. It seems strange 

 that this important relation has thus far eluded search, and 

 that little is known beyond the ingenious surmises of 0. E. 

 Meyer and the empiric law of my own. Inasmuch as the time 

 of transpiration varies nearly as the 5/3 power of absolute 

 temperature, the sensitiveness of the method is obvious. 



Phys. Lab., U. S. G. S., 

 Washington, D.C. 



II. The " Elastic Medium " Method of treating Electrostatic 

 Theorems. ByW. H. Beagg, M.A., Professor of Mathe- 

 matics in the University of Adelaide, South Australia*. 



IT is usual to deduce the ordinary theorems of electro- 

 statics from the law that two amounts of electricity repel 

 one another with a force proportional directly to the product 

 of these amounts and inversely to the square of the distance 

 * Communicated by the Author. 



