ix 



June 20, 1872. 



Page 



• Preliminary Note on the Reproduction of Diffraction-gratings by means of 



Photography. By the Hon. J. W. Strutt, M.A 414 



On the 26-day Period of the Earth's Magnetic Force. By J. A. Broun, 

 F.R.S 417 



Contributions towards the History of the Ethylene Bases. By A. W. 

 Hofmann, Ph.D., F.R.S., Professor of Chemistry in the University of 

 Berlin 425 



Colouring-matters derived from Aromatic Azodiamines. By A. W. Hof- 

 mann, Ph.D., F.R.S., and A. Geyger, Ph.D 431 



On the present amount of Westerly Magnetic Declination [Variation of the 

 Compass] on the Coasts of Great Britain, and its Annual Changes. By 

 Staff Captain Frederick J. Evans, R.N., F.R.S., Hydrographic Depart- 

 ment of the Admiralty (in charge of Magnetic Department) 434 



Notice of Further Researches among the Plants of the Coal-measures. By 

 Prof. W. C. Williamson, F.R.S 435 



Volcanic Energy : an attempt to develope its true Origin and Cosmical 

 Relations. By Robert Mallet, F.R.S 438 



On some Properties of Anhvdrous Liquefied Ammonia. By G. Gore, 

 F.R.S 441 



On the Physical Nature of the Coagulation of the Blood. Bv Alfred 

 Hutchison Smee, F.C.S., F.S.S 442 



On the Detection of Organic and other Nitrogenized Matter existing in the 

 Atmosphere. By Alfred Hutchison Smee, F.C.S., F.S.S 442 



Contributions to Terrestrial Magnetism. — No. XHI. By General Sir 

 Edward Sabine, K.C.B., V.P.R.S 443 



On the Law of Extraordinary Refraction in Iceland Spar. By G. G. Stokes, 

 M.A., Sec. R.S 443 



On a Voltaic Standard of Electromotive Force. By Latimer Clark, 

 M.I.C.E 444 



No. 137. — June 20, 1872 (continued). 

 Pyrology, or Fire Analysis. By Capt. W. A. Ross, R.A 449 



On the Action of Electricity on Gases. By Sir B. C. Brodie, Bart., F.R.S., 

 Hon. D.C.L. Oxon., late Waynnete Professor of Chemistry in the 

 University of Oxford 472 



Researches on the Atomic Weight of Thallium. Bv William Crookes, 

 F.R.S. &c 475 



On the Spectrum of Nitrogen. By Arthur Schuster, Student at the Physical 

 Laboratory of Owens College 484 



On the Combined Action of Heat and Pressure upon the Paraffins. By 

 T. E. Thorpe and John Young, of the Andersonian University, Glasgow. 488 



On the Echinidea of the ' Porcupine ' Deep-sea Dredging-Expeditions. By 

 Prof. Wyville Thomson, LL.D., D.Sc, F.R.S 491 



