VOL. LXXXII.] PHILOSOPHICAL TRANSACTIONS. 221 



The Transactions of the r s. give an account of the earthquakes in the 

 northern parts of England, in the years 1703 and 1750. That of the latter 

 year is described (Phil. Trans, vol. 40) as "beginning in Derbyshire, and passing 

 off the island, through Lincolnshire and part of Cambridgeshire, its direction 

 being from west to east." From the preceding narrative it appears, that nearly 

 the same tract of country was affected by the late concussion, and that it came 

 in the same direction from west to east; circumstances which correspond with the 

 observations of Mr. Michel); 1st. " That the same places are subject to returns 

 of earthquakes at different intervals of time;" — 2dly, That earthquakes gene- 

 rally come to the same place from one and the same point of the compass." 

 These, and other facts, that ingenious philosopher adduces in support of his 

 hypothesis, that earthquakes are caused by the steam raised by waters, contained 

 in the cavities of the earth, suddenly rushing in on subterraneous fires; which 

 steam, the moment it is generated, insinuates itself between the strata of the 

 earth, and produces the undulatory motion before-mentioned. It may however 

 be remarked, that the state of the air, before the shock, was calm, close, and 

 gloomy, such as is described by Dr. Stukeley as necessary to prepare the earth to 

 receive an electrical stroke, and the circumstance of its having been partially 

 felt in the same room may be supposed to favour that hypothesis; but yet the 

 concussion seems not to have been so strong on the eminence at Belvoir Castle 

 as it was in the neighbouring vale. 



XF. Experimenls made with the Fieiv of Decompounding Fixed ^ir, or Carbonic 

 ylcid. By George Pearson, M. D., F. R. S. p. 289. 

 From a paper read to the Phil. Soc. of Edinb. in 1735, published in the 2d 

 vol. of the Phys. and Lit. Essays, it appears that Dr. Black had discovered the 

 affinities between an aeriform substance, which he called fixed air, and alkalis, 

 quick-lime, and magnesia. His experiments also showed, that many properties 

 of these bodies depended on the union and separation of this air. The discovery 

 of these facts established this elastic fluid to be a peculiar species of substance. 

 Mr. Cavendish, Dr. Brownrigg, Dr. Priestley, Sir Torbern Bergman, Mr. 

 Bewley, Mr. Kirwan, and other chemists, afterwards extended, very consider- 

 ably, the history of fixed air. The question whether it was a simple or com- 

 pound body was discussed; and by many persons it was believed to have been 

 proved, that fixed air was composed of phlogiston and respirable air. But some 

 of the principal facts, on which this belief was founded, being afterwards demon- 

 strated to be erroneous; and the production of fixed air being, to the apprehen- 

 sion of many chemists, more satisfactorily accounted (or by the new principles 

 of chemistry, this doctrine of its composition became no longer tenable. As 

 the science of chemistry advanced, many acids were demonstrably proved to con- 



