246 Mr. J. E. Cullum. Report of Absolute Magnetic [Apr. 12, 



perature coefficients are much smaller in each case. With the exception 

 of carbonate of soda and chrome alum, all the other hydrated salts have 

 a coefficient of expansion not differing greatly from that of ice at low 

 temperatures. Generally, the densities of the compressed blocks of 

 different bodies agreed well with the results of other observers, but 

 my potash alum had only a density of 1*614, whereas Playfair and 

 Joule give 1*731. It will be noted that iodoform is a highly expan- 

 sive body like iodine, and that oxalate of methyl has nearly as great 

 a coefficient as paraffin, which is one of the most expansive solids. The 

 correcting factor was used for paraffin, naphthalin, chloral hydrate, 

 iodoform, and sodium. All weights are in grammes. 



It will be possible by cooling the moulds with liquid air during the 

 process of hydraulic compression, to produce cylindrical blocks of solid 

 bodies of lower melting-points than any given in this investigation, 

 such as alcohol, ether, nitrous oxide, ammonia, chlorine, &c, and to 

 ascertain their coefficients of expansion in the solid state between the 

 individual melting-points and the boiling-point of liquid air. 



This method, which works well with liquid oxygen or air, fails 

 when applied to liquid hydrogen, as the density of the liquid is too 

 small (apart from other difficulties) to give accurate values of the 

 weights of fluid displaced. For temperatures about 20° absolute, re- 

 course must be had to measurements of the coefficient of linear 

 expansion, and such observations could only be applied with ease to 

 metallic bodies and alloys. 



' ; Eeport of Absolute Magnetic Observations at the Valencia 

 Observatory (Cahirciveen, co. Kerry), 1899, 1900, and 1901." 

 By J. E. Cullum. Communicated by The Earl of Bosse, 

 F.E.S. Eeceived April 12— Eead April 24, 1901. 



As far back as 1887 the late Professor FitzGerald, of Trinity College, 

 Dublin, expressed a desire for a series of magnetic observations to be 

 made in Ireland, when the writer offered to undertake the work if he 

 was provided with instruments, and obtained, the consent of the 

 Meteorological Council. This was done, and an old pattern unifilar by 

 Jones, with a dip circle by Barrow, being loaned by Trinity College, 

 experimental observations were commenced in a wooden hut erected in 

 the Observatory grounds in Valencia Island, with funds supplied by 

 the Eoyal Irish Academy. The result of the first few years of this 

 series was published in the ' Proceedings of the Eoyal Irish Academy,' 

 and the observations were continued until the end of 1896. The 

 observatory was removed in 1892 to Cahirciveen, about 4 miles 

 eastward. 



