June 9, 1892] 



NATURE 



141 



Table I. — Iron IVire^ dianutero'T$ mm. 



For the sake of easy comparison, the principal results obtained 

 with this wire are collected in Table II. 



Table II. — Iron Wire, diameter o-J^ mm. 



Similar experiments were afterwards made with nickel and 

 cobalt. 



A nickel wire was used, the diameter of which was 0'65 mm. 

 The retractions which it underwent in fields of gradually in- 

 creasing strength are given in the second column of Table III. 



The retractions of the wire when carrying a current of i am- 

 pere, are given in the third column of the table. Remembering 

 that the figures in the second and third columns denote 

 millionths of a centimetre, the close agreement between the two 

 is very remarkable. Such small discrepancies as exist can hardly 

 be entirely accounted for by observational or instrumental errors ; 

 they are probably mainly due to the effect of the rise of tem- 

 perature (2° -6 C.) caused by the current in diminishing the sus- 

 ceptibility of the nickel. 



NO. I 1 80, VOL. 46] 



Tension has a large effect upon the magnetic retraction of 

 nickel : it is, therefore, the more remarkable that the action of a 

 current, which operates, so markedly upon iron, should in nickel 

 be practically insensible. 



The results with no current obtained for a strip of rolled 

 cobalt, the length of which between the clamps was lo cm., and 

 the cross section 1*82 sq. mm., are given in the first two columns 

 of Table IV., and those with a current of 2 amperes in the third 

 column. 



Table W.— Cobalt Strip, section 182 sq. mm. 



From an inspection of the differences tabulated in the fourth 

 column, it appears that the effect of the current is to increase the 

 retraction very slightly. 



According to Rowland the susceptibility of cobalt is increased 

 by heating. The small additional retraction indicated when the 

 current was passing was, therefore, no doubt due to the increased 

 susceptibility consequent upon current heating. It may be 

 noted that tension seems to have no material effect upon the 

 i magnetic retraction of cobalt. 



Summary. 



In an iron wire carrying a current, the maximum magnetic 

 elongation is greater, and the retraction in strong fields is less, 

 than when no current is passing. The effect of the current is 

 opposite to that of tension. 



The magnetic retractions of nickel and of cobalt are not 

 sensibly affected by the passage of a current through the metals. 

 (Tension considerably modifies the magnetic retraction of nickel, 

 but not that of cobalt.) 



"The Human Sacrum." By A. M. Paterson.M.D., Professor of 

 Anatomy in University College; Dundee, St. Andrews University. 

 Communicated by Prof. D. J. Cunningham, D.Sc, F.R.S. 



Chemical Society, May 19. — Prof. A. Crum Brown, F.R.S., 

 President, in the chair. — The President announced that the 

 Council had adopted a resolution expressive of the loss the 

 Society and chemists generally had suffered by the death, on 

 May 5, of Prof, von Hofmann. The resolution would be 

 communicated to the family of the deceased, and to the German 

 Chemical Society. — The following papers were read : — The 

 magnetic rotation of compounds supposed to contain acetyl, or 

 of ketonic origin, by W. H. Perkin. The author draws at- 

 tention to Briihl's determination of the refractive powers of ethyl 

 acetoacetate, which favours a ketonic constitution, and to its 

 magnetic rotation, which was determined some years ago by 

 himself, and which also supports this view. A list is then given 

 of seven supposed acetyl compounds, of which he has ascer- 

 tained the magnetic rotation, all giving numbers pointing to a 

 ketonic constitution. As such compounds as these behave some- 

 times as ketonic and sometimes as hydroxy-derivatives, it was 

 thought desirable to examine a larger number of compounds 

 supposed to contain acetyl, or of ketonic origin, between wide 

 limits of temperature. The following were selected : pyruvic 

 acid, levulinic acid (fused and in solution), ethyl acetonedicar- 

 boxylate, ethyl acetoacetate, acetylacetone, methylacetylacetone, 

 and ethyl )8-amidocrotonate. The last-mentioned four were 

 examined at widely different temperatures. The magnetic 

 rotations of the first five .substances agree with a ketonic con- 

 stitution, though that obtained for ethyl acetonedicarboxylate is 

 rather high. The rotation of acetylacetone is very high, showing 

 it to be an unsaturated or hydroxy-compound, whilst the value 

 obtained for methylacetylacetone stands between the hydroxy 

 and ketonic rotations. At temperatures near 100°, however, 

 these compounds give much lower rotations than when cold^ 



