98 REPORTS ON INVESTIGATIONS AND PROJECTS. 



(10) Neutral contacts and switches. (Abstract.) Walter P. White. Phys. Rev., 30, 



784. 1910. 



By neutral contacts is meant contacts free from electromotive forces, due 

 to small temperature difference. Such contacts are often advantageous and 

 can usually be obtained with ease where extremely low resistance is not 

 necessary. One simple way of obtaining them is to make the contacts be- 

 tween very thin strips of homogeneous metal. Contacts of this type can 

 easily be given a wide variety of forms, some of which, besides their supe- 

 riority in the matter of electrical results, are much more convenient and 

 cheaper than forms now in common use. 



(11) The relation between zero shift and size of wire in the moving coil galvanometer. 



(Abstract.) Walter P. White. Phys. Rev., 30, 782. 1910. 



The displacement of the zero usually produced by the deflection of a mov- 

 ing coil galvanometer is at present one of the most serious sources of incon- 

 venience or error with that instrument. It is due to magnetic impurity in 

 the coil and to irregularity of the magnet field, and the entire avoidance of 

 these two defects is practically impossible. Hence it is worth while to con- 

 sider how their effect may be diminished. The paper shows that for given 

 magnetic defects the zero shift increases with the sensitiveness and also with 

 the shortness of period, but diminishes when period is shortened at the ex- 

 pense of sensitiveness ; for a galvanometer of given performance it increases 

 with the amount of dead material in the coil, and very rapidly with the size 

 of wire. Hence low resistance, which necessitates large wire, increases zero 

 shift, and an unnecessarily low resistance is decidedly detrimental. Hence, 

 also, in ballistic work it is often better to get long periods by using wide coils 

 than by loading narrow ones. 



(12) Heizmikroskope. Arthur L. Day and Fred. Eugene Wright. Centr. f. Min., etc., 



No. 13, 423. 1910. 



A brief answer to certain criticisms by C. Doelter (Vienna) of the new 

 thermal microscope constructed in the Geophysical Laboratory. The appear- 

 ance of the criticism seemed to afford a favorable opportunity to explain 

 some of the advantages of this instrument for use in quantitative research 

 work, when compared with earlier instruments employed for a similar pur- 

 pose. 



(13) The platinum-rhodium thermoelement from o° to 1755°. Robert B. Sosman. Am. 



Journ. Sci. (4), 30, 1. 1910. 



In continuation of the recent work from the Geophysical Laboratory 

 on the nitrogen thermometer from zinc to palladium (see page 93), the 

 interpolation curve of the thermo-element Pt-(90 Pt 10 Rh), has been ex- 

 tended downward to o° and upward to the melting-point of platinum. The 

 value of the melting-point of platinum obtained by extrapolation of the 

 curves of a number of thermo-elements containing from 1 to 15 per cent 

 rhodium confirms the value previously adopted (1755 ) within the estimated 

 limit of 5 . A simple method of interpolating temperatures with the 10 per 

 cent thermo-element by means of a standard curve and deviation curves is 

 described in the article. 



The variation of thermal E. M. F. with the temperature and composition 

 of the platinum-rhodium alloy wire has been determined. The variation, 



