458 Royal Society, 



the author observes, are not greater than usually occur in chemical 

 reactions, in consequence of the uncertainty that exists with regard 

 to the accurate proportions of chemical equivalents. He points out 

 various circumstances in experiments of this nature, which tend to 

 affect the results and lead to inaccurate conclusions, if care be not 

 taken to guard against these sources of error. One of the principal 

 of these is the heat which is generally evolved by the separation of 

 a base, or new compound, in a solid form : and the author discusses 

 the influence of this change on the results deduced from his experi- 

 ments. He considers that these experiments sufficiently establish the 

 general principle announced in the beginning of his paper. 



A supplementary note is added on the determination of the Spe- 

 cific Heat of Fluids. 



January 11, 1844* — " An Account of a slight Shock of an Earth- 

 quake felt in the Channel Islands." By J. Elliott Hoskins, M.D., 

 F.R.S. : in a Letter to P. M. Roget, M.D., Sec. R.S., &c. Commu- 

 nicated by Dr. Roget. 



The phenomena described in this letter occurred simultaneously in 

 Jersey, Guernsey, Alderney, Serk, Heme, and Jethore. On Friday, the 

 22nd of December, at seven minutes before 4 p.m., a noise resembling 

 a distant thunder-clap was heard ; this was immediately followed by 

 sounds as of a railroad carriage rumbling over an irregular metallic 

 surface ; it was accompanied by distinct undulatory motion. This 

 again was succeeded by a shock; the whole lasting from 10 to 15 

 seconds. The barometer was uninfluenced, standing at 30*354 : a 

 light wind prevailed, varying from S.S.E. to S.S.W. During the 

 whole of the month the air had been peculiarly still, and the baro- 

 meter uniformly high ; the maximum, up to the above date, having 

 been 30*518, the minimum 30*042. The thermometer had ranged 

 throughout the month, from 47° to 52° during the day, and from 

 45° to 49° during the night. 



Hundreds of persons agree as to having experienced a distinct 

 shock, their impressions varying according to the positions occupied 

 by the observers. Those inhabiting the solid granite structures of 

 the lower town conceived that heavy masses of furniture were over- 

 turned and moved in the apartments above or below them: they 

 were not, however, so conscious of vibratory motion as those in the 

 less substantial houses of the upper part of the town, or as those in 

 the open air. In many houses, this vibratory motion was so violent as 

 to cause much alarm, and was accompanied by crashing sounds, as 

 though roofs and chimneys were falling ; in some instances, chimney- 

 pots were thrown down ; suspended lamps were observed to wave ; 

 bells rang spontaneously ; the vane of the town church waved, and 

 one of its bells struck twice. 



Persons in the open air were sensible of an undulatory motion, 

 tending from the S.W., which occasioned unsteadiness of footing, 

 and in some cases a transient feeling of nausea. A steam-engine in 

 the Serk mines was remarked to suspend one out of its usual five 

 strokes per minute ; the engineer was alarmed lest this should be a 

 precursor of bursting of the boiler. The massive granite works of 



