190 Dr. J. R. Rydberg on a certain Asymmetry 



Analogously the latter must show decidedly smaller com- 

 pressibility than the organic body, and hence it follows that 

 whereas the lower critical pressure (solid -liquid) of naphtha- 

 lene, for instance, lies in the region of some 10,000 atmospheres 

 in my experiments, the corresponding (critical) pressure of 

 the rock magma will be indefinitely higher. 



From this, however, it is by no means to be inferred that 

 the relation of melting-point to pressure (dOjdp) will be 

 different in the silicate and in the carbon compound. In the 

 latter case data for normal fusion are available for wax, 

 paraffin, spermaceti, and naphthalene. These lie within a 

 margin of '020 to '036. Taken into consideration with the 

 difficulty of obtaining these data, the preliminary character 

 of the experiments, the lack of crystalline deflniteness in many 

 of the compounds, and the fact that even for the same sub- 

 stance* the coefficient may vary as much as # 027 to "035, the 

 said margin may reasonably be regarded as narrow. It 

 appears to me probable, therefore, since fusion in the organic 

 bodies and the silicate is alike in type, that the same factor 

 d0/dp will correspond to both cases. 



Direct evidence in favour of this view will be adduced in 

 my next paper. 



XXIII. On a certain Asymmetry in Prof. Rowland's Concave 

 Gratings. By Dr. J. R. Rydbekg, Docent of Physics at 

 the University of Lund, Sweden f . 



I. TN order more especially to obtain a series of observations 

 _L fitted for a continuation of the studies on the spectra 

 of the elements, of which the commencement has been pub- 

 lished in my " Recherches sur la constitution des spectres 

 lineaires des elements chimiques " (K. Svenska Vetensk. Akad. 

 Handl. Bd. xxiii. No. 11), a spectroscope with one of Prof. 

 Rowland's concave gratings (10,000 lines to the inch) was 

 procured for the Physical Institution of the University of 

 Lund. It was mounted in a most excellent manner by the 

 Mechanician of the Physiological Institution, Hilding Sand- 

 strom, according to the instructions of Prof. Rowland {see 

 Ames, Johns Hopkins University Circulars, viii. Xo. 73, 

 May 1889 ; Phil. Mag. [5] xxvii. p. 369), but with full 

 freedom in the details of construction. The adjustments 

 also were executed according to the same instructions, but 



* See my work for Naphthalene in American Journal, xlii. p. 144, 

 el seq., 1891. 



f Communicated by the Author. 



