384 Analyzes of Books. [Nov* 



consider as radiation, he affirms to be nothing more than pulses 

 of the air, similar to the undulations by which sound is propa- 

 gated ; these undulations may be either of heat or of cold, ac- 

 cording as they proceed from a heated or a cooled surface. 

 Accordingly, the amount of these pulses, or what is called the 

 radiation of heat, differs according to the gas through which 

 the pulsation takes place. In hydrogen gas it is much greater 

 than in air, and in a complete vacuum it would disappear alto- 

 gether. Nothing can be more ingenious than his views on this 

 subject, nor than the instrument which he has contrived for mea- 

 suring the pulses of cold emitted from a clear sky. But as, 

 after reading over his paper with some attention, I have not been 

 able to see clearly the evidence on which his opinions are 

 founded, I think that the best way to do justice both to Mr. 

 Leslie and to the readers of the Annals will be to print his paper. 

 It wiil appear, therefore, in an early number. 



VIII. A Method of determining the Time with Accuracy, 

 from a Series of Altitudes of the Sun, taken on the same Side of 

 the Meridian. By Major-General Sir Thomas Brisbane, Knt. 

 F.R.S.E. 



Sir Thomas Brisbane having been moving much about for a 

 number of years, was unable to carry with him large astrono- 

 mical instruments ; he was induced in consequence to try how 

 good results he could obtain from small instruments. His 

 success has been such as to induce him to recommend the 

 sextant as an instrument which would be much more employed 

 by astronomers if its value were known. In this paper he shows 

 his method of determining the time from a series of altitudes of 

 the sun on the same side of the meridian. This method he 

 recommends as fully as exact as the method by equal altitudes, 

 and as more exact than that method when a change of tempe- 

 rature has taken place in the interval between the forenoon and 

 afternoon observations. For the method itself we must refer to 

 the paper, as it could not be made intelligible without tran- 

 scribing the whole calculation. 



IX. Observations on the Junction of the Fresh Water of Rivers 

 with the Salt Water of the Sea. By the Rev. John Fleming, 

 D.D. F.R.S. Edin. As the specific gravity of salt water is 

 greater than that of fresh, Dr. Fleming naturally conjectured 

 that when the tide begins to flow up the mouth of a river, the 

 salt water will occupy the bottom of the channel, and will be 

 covered by the fresh water which will occupy the surface. A 

 set of trials made on the waters of the Frith of Tay at different 

 times of the tide, fully confirmed the accuracy of his opinion. 

 Mr. Stevenson made similar observations on the waters of the 

 Don, but he found this not quite the case with the Thames. 

 From his trials on that river he was led to infer that the fresh 

 water moves backwards and forwards without any real flow into 

 the sea. 



X. Memoir of the JJfe and Writings of the Hon. Alexander 



