A. Dumoard — Temperature Coefficients, etc. 245 



the scale at a meter's distance was obtainable with a current 

 of 0*000,000,000,5 of an ampere. At present, under such 

 circumstances, a similar deflection would be obtained with 

 0*000,000,000,0012 ampere, that is to say, the apparatus is 

 about 400 times as sensitive as it was when first described. 



At present, the boldmetric apparatus under the conditions 

 already cited, will indicate a change of temperature in its strips 

 of at any rate much less than one-ten-millionth of one degree 

 centigrade. 



Smithsonian Institution, Washington, Feb. 1898. 



Art. XXXI. — On the Temperature Coefficients of Certain 

 Seasoned Hard Steel Magnets ; by Arthur Durward. 



In a paper* published last year, Prof. B. O. Peirce gave the 

 induction coefficients of a large number of glass-hard magnets 

 made of different kinds of steel and carefully seasoned in the 

 manner describedf by Messrs. Barus and Strouhal. These 

 magnets being at my disposal, it seemed to me that a series of 

 measurements of their temperature coefficients might yield 

 interesting results, since it is often desirable to know the com- 

 parative effects of slight changes of temperature upon the 

 moments, of magnets of different shapes used in determining 

 the strengths of magnetic fields. I had not been able to dis- 

 cover that any one else had experimented upon so large a 

 variety:); of stout seasoned magnets, and I hoped that the 

 results might be sufficiently uniform to indicate some relation 

 connecting the temperature coefficients of such magnets, made 

 of a given kind of steel, with their dimensions. Some of the 

 tables printed below show very approximately what this rela- 

 tion is for certain brands of steel. The temperature coefficients 

 of two magnets of the same dimensions and material, however, 

 sometimes differed so widely that the results did not seem 

 capable of any very definite interpretation. This was espe- 

 cially true in the case of a large set of magnets made of twice 



* This Journal, November, 1896. 



f Bulletin of the U. S. Geological Survey, No. 14, 1885. 



% L. Dufour, Pogg. Ann., xcix, 1855 ; Holmgren, Acta Soc. Scient. Upsala, 3, i, 

 18a6; Gore. Phil. Mag. (4), xl, 1870; Unverdorben. Inauguralschrift, 1866; 

 Gordon and Newhall, Phil. Mag. (4), xlii. 1871 ; Marshall, Proc. Edin. Soc, vii, 

 1873; Jamin, Mondes, 2, xxxiii, 1873; Wild , Carl's Repert . ix, 1873; Fave, 

 Comptes Rendus. lxxxii, 1876; Gaugain. Comptes Rendus, lxxxii; Poloui, Natur- 

 forscher. xiii. 1880; Trowbridge, this Journal, 1881 ; Poloni, Beiblatter, v, 1881; 

 Poloni, Journ. de Physique, 2, ii, 1883; F. Kohlrausch, Wied. Ann., xxii, 1884; 

 Berson, Journ. de Physique, 2. v, 1886; Ledeboer. Journ. de Physique, 2, vii; 

 Chistoni, Mem. Modena, 2, ix, 1893 ; Cancani, Atti. Ace. Lincei, 1887. 



