99 



A Method of Measuring the Absolute Dilatation of Mercury. 



[Abstract.] 

 By Arthur L. Foley. 



The forms of apparatus used by Duloug and Petit, and Regnault, in 

 determining the absolute dilatation of mercury are open to one or both 

 of the following- objections: (1) Some parts of the mercurj^ columns are 

 exposed and so the termperature can not be exactly the same throughout; 

 (2) the heights of the columns must be measured from some assumed 

 point of equilibrium in a horizontal connecting tube. The method pro- 

 posed in this investigation is entirely free from both these objections. 



The two arms of a vertical U tube are jacketed in the usual way, 

 except that the jacketing tubes are of glass to permit the heights of the 

 mercury columns to be taken with a cathetometer, at any level. Into 

 the tube is poured a quantity of mercury sufficient to stand several centi- 

 meters high in each arm. "When the required temperature has been 

 attained the two heights are carefully measured. More mercury is added 

 and under the same temperature conditions the heights are again meas- 

 ured. The differences in the heights before and after adding the mercury, 

 together with the temperature difference of the two arms, are all the 

 data required. Many independent determinations may 1;e made by adding 

 or removing mercury. As the readings are in every case difference 

 readings any effects that might come from capillary and convection 

 currents in the horizontal tube are eliminated. Two of my students, 

 J. G. Gentry and O. A. Rawlins, have obtained remarkably consistent 

 results by this method, though the coefficient of dilatation obtained by 

 them is slightly less than that obtained by Regnault. 



The Geodesic Line of the Space ds^=dx^-j-s'm^xdy'-\-dz^. 



By S. C. Davisson. 



