proceedings: philosophical society 499 



in which nt denotes the mass contained within the sphere of radius r, 

 and h is a constant. 



The results of this operation show that it is impossible to account 

 for all of the excess density in the interior by compression alone. It 

 does account for a surprisingly large part of it, however. The differ- 

 ence must be attributed to a segregation toward the center of heavy 

 material, presumably metallic iron, and we thus have a quantitative 

 measure of the amount of this segregation. 



Finally, mention is made of the fact that from the center of the 

 earth out to about 0.5 of the distance to the surface, the properties of 

 the material composing this central portion of the earth are such that 

 transverse vibrations are not transmitted. This part of the earth, 

 therefore, is lacking in rigidity; in other words, it is not a solid and 

 therefore must be considered in spite of its high density to be either a 

 gas or a liquid, depending on whether or not the temperature is above 

 the critical point, liquid-vapor, of the material. 



Both the above papers were illustrated by lantern slides. 



Discussion. — Both the above papers were discussed after the read- 

 ing of the second, Messrs. Beall, Spencer, Bowie, Lambert, Humph- 

 reys, Todd, Hawkesworth, and Sosman participating in the discussion. 



The last paper of the evening by Messrs. H. C. Dickinson and 

 C. H. Meyers on A ly atmosphere manometer and a lOO-atmosphere 

 piston gage was presented by Mr. Dickinson. 



A fifteen-atmosphere mercury manometer and a one hundred-atmo- 

 sphere piston gage were described. The manometer consists of five 

 glass U-tubes 250 cm. long, connected in series, each of which may be 

 by -passed by a valve. Four of these tubes may be used to measure 

 multiples of three atmospheres, while any fraction of three atmospheres 

 may be measured on the fifth. To avoid rusting of steel parts and 

 fouling of mercury surfaces, pure ethyl alcohol is used to transmit 

 the pressure, between tubes. The pressure transmitting liquid may be 

 admitted into the manometer between any two U-tubes. The tem- 

 perature of the manometer is measured by a thermometer which has 

 a bulb located behind the center of the manometer and of the same 

 length as the U-tubes. The accuracy of the manometer-temperature 

 measurement is improved by an air circulating fan which keeps the 

 room temperature very uniform. 



The piston gage consists of a hardened steel piston of approximately 

 one square centimeter area, floating on oil inside a hardened selel cylinder. 

 A dead weight load is applied to this piston through a plunger specially 

 designed to transmit only a vertical force component to the piston. 

 For the purpose of cutting down leakage past the piston at higher 

 pressures, the cylinder has been made with a re-entrant part which 

 encircles the piston so that the pressure is applied to the outside as well 

 as the inside of the cylinders. A mechanical device has been applied 

 which rotates the piston slowly, without producing any uncertain 



