336 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Measurements of compressibility or of change of volume during freez- 

 ing, as in two following papers, demand this property of freedom from 

 leak. 



The method of pressure measurement adopted here, and which secures 

 freedom from leak, has already been described by Lisell.* He meas- 

 ured the effect of pressure on the resistance of manganin wire, and 

 proposed that the change of resistance be used as a measure of pressure. 

 Lisell found the effect of pressure between and 4200 atmos to be 

 linear, and showed that there was no appreciable temperature effect 

 between 0° and room temperature. But Lisell also showed that diff"er- 

 ent specimens of manganin show slightly different pressure coefficients, 

 so that the advantage of reproducibility must be given up. Lately, 

 Lafay ^ has also measured the pressure effect on manganin up to 3500 

 kgm. and has found nearly the same pressure coefficient as did Lisell. 



The data of this paper show by direct comparison with the absolute 

 gauge that the manganin is suitable as a pressure gauge over much 

 wider ranges of pressure. Up to 13,000 kgm. the relation is linear 

 within the errors of the absolute gauge. It would not have been sur- 

 prising if this had not been true, in view of the fact that manganin has 

 a pressure coefficient which is positive instead of negative like that of 

 all the pure metals. Furthermore, over this pressure range the read- 

 ings are entirely free from hysteresis or creep. This is opposed to the 

 work of Lussana,* who found various temporary effects after the appli- 

 cation of pressure. His results have not been verified by subsequent 

 observers, however, and the entire absence of the effect here under a 

 very much wider pressure range would seem to make pretty certain 

 that there was some obscure source of error in Lussana's work. 



The manganin used in this work was of German manufacture. No. 38, 

 double silk covered, of about 30 ohms to the meter. With change of 

 temperature it shows a maximum resistance at about 27°. The coils 

 were of about 100 ohms resistance, the wire being wound non-induc- 

 tively on itself in the form of a toroid, about 1 cm. in diameter and 

 5 mm. thick. To protect the wire, the toroid was covered with a wind- 

 ing of fine silk ribbon, only the ends of the wire being exposed in order 

 to make connections with the insulating plug. This plug was of the 

 same design as that shown in the previous paper, except that it was 

 made of hardened nickel steel instead of tool steel. 



' Lisell, Om Tryckets Inflytande pS. det Elektriska Ledningsmotstandet 

 hos Metaller samt en ny Metod att Mata Hoga Tryck (Diss. Upsala, 1903) 

 3 Lafay, C. R., 149, 566-569 (1909). 

 * Lussana, Nuov. Cim., 10, 73-84 (1899); 5, 305-314 (1903). 



