Reply to Mr. Cooper's Queries. 295 



which in time takes place in the freezing point of thermome- 

 ters, has published a memoir on Shooting Stars, in which he 

 supports the theory, that those meteors are caused by the com- 

 bustion of trains of inflammable gases or vapours in the at- 

 mosphere. He thinks that such trains may exist in the higher 

 regions without being dissipated, in consequence of the general 

 and perfect tranquillity which may be considered as reigning 

 there : and he endeavours to combat the difficulty generally 

 urged against this theory,— the diminished inflammability by 

 expansion of gaseous or vaporous mixtures, — by referring to 

 the vapour of phosphorus; stating, " that phosphorus becomes 

 luminous, or suffers a slow combustion, at a temperature so 

 much the lower as the quantity of oxygen gas in a determinate 

 space is rendered smaller, either by mixture with other gases, 

 or by rarefaction." He then ventures the conjecture, that 

 there may be other substances, capable by natural operations 

 of being reduced to the state of vapour or gas, and which, 

 though not inflammable at common temperature and pressure, 

 may become so by being elevated in the atmosphere*. 

 [To be continued.] 



XLIX. Reply to Mr. Samuel Cooper's Queries onjinding 

 the exact Mean Solar Time. 

 To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 

 TN the last number of your Magazine, pages 210 and 211, 

 x there is a curious solution of Mr. Samuel Cooper's for find- 

 ing Mean Solar Time by an altitude of the sun, taken with a 

 reflecting circle and an artificial horizon : also some queries 

 as to the accuracy of his method, &c. I beg to observe that al- 

 though it appears to me to be rather an awkward and far-fetched 

 form, involving unnecessary trouble, yet with the reduced la- 

 titude, as Mr. C. terms it, the sun's reduced declination, and 

 his true altitude, he has succeeded in bringing out the mean 

 time within l s -6 of what it is by the first method given in the 

 third edition of Mackay's work on the Longitude, &c. page 

 126; or by the second method in Norie's Navigation. lie 

 will find either of these methods shorter and more expeditious 

 fur finding apparent time, at the same time they are better 

 known by mathematicians. Mr. Cooper's phrases, " apparent 

 and visihlr latitude, and visihk altitude" are not scientifically 

 expressed ; therefore 1 1 1 < • \ OUghl to be avoided, to prevent any 



ambiguity in die expressions of their sexagesimal quantities; 



From the substance of the question 1 make the latitude of 



• Journal of Science, &c, vol. xv. p. 391. 



Pertenhall, 



