Mr. T. Hopkins on the Meteorology of Bombay. 467 



cupies no space in solution. The solution which corresponds 

 to this turning-point has a chemical strength of about 50°, 

 and a specific gravity of nearly 1*05. Were a solution of sul- 

 phate of magnesia to be carefully made with proportions of 

 salt and water corresponding to this stage of dilution, the re- 

 sult would appear to corroborate the late experiments of 

 Dalton and of Messrs. Playfair and Joule, and thus a very 

 accurate experiment might be made to support a very falla- 

 cious theory. 



This last remark applies equally to many other substances 

 whose examination is described in this memoir, and it shows 

 the danger of drawing a sweeping conclusion from the results 

 of any single experiment, however accurately performed. 

 Thus, in the case of sulphuric acid, if we were to adopt the 

 rash principle of deciding upon the atomic measure from the 

 results of a single experiment, we could prove the atomic 

 measure of that acid to be 2 volumes, or 1 volume, or nothing, 

 or less than nothing ; in short, anything we pleased between 

 plus 34 septems and minus 68 septems; for we could pick 

 out an accurate experiment to yield any numerical product 

 that best suited a given purpose within those limits. 



LXV. Observations on a Paper entitled " Some Points in the 

 Meteorology of Bombay " read by Colonel Sabine to the Bri- 

 tish Association in 1 845, and published in the Philosophical 

 Magazine for January 1846. By Thomas Hopkins, Esq.* 



"Y/I7TTH our imperfect knowledge of the influences which 

 7,y determine the general movements of the atmosphere, 

 the semi-diurnal fluctuations of the barometer become inter- 

 esting objects of study, as it appears not improbable that 

 the causes which produce the daily alterations of that instru- 

 ment may determine its casual and irregular fluctuations, as 

 well as the general movements of the atmosphere itself. 



That the diurnal fluctuations of the barometer are in some 

 way connected with alterations of temperature, is apparent 

 from their relation to the daily variation of solar influences ; 

 but the precise way in which these influences operate is not 

 equally clear. A rise of temperature, such as that which lakes 

 place in the morning, there can be no doubt tends in some 

 degree to lighten the atmosphere, and to produce a fall of the 

 barometer in the part ; but at the same time it increases eva- 

 poration of aqueous vapour from wet surfaces, the effect of 

 which is to add to the weight of the whole atmosphere in the 

 locality, to the extent of the addition of the vapour that is 

 * Communicated by the Author. 



