162 



REPORT — 1839. 



the distance from the equator ; and Professor Forbes, in his 

 excellent paper on the Horary Oscillations of the Barometer 

 near Edinburgh, has given a formula which apphes with con- 

 siderable accuracy to such observations as have been yet made; 

 and although, as we have seen, considerable variations from the 

 mean may arise from the times and seasons of such observa- 

 tions, nevertheless the author has evinced admirable philoso- 

 phical tact in his method of treating the subject, and has for- 

 tunately selected for his term of comparison the semi-mean 

 oscillation between 10 and 4 p.m., which perhaps, upon the 

 whole, may be found to give a tolerably fair approximation. 

 The question, however, must still be considered in its infancy, 

 and but little investigated by the powerful aid of contemporary 

 and long continued hourly observations in different latitudes. 

 It would therefore, at present, be useless to enter upon a dis- 

 cussion of the anomalies alluded to by Professor Forbes in the 

 observations hitherto made at different places. Thus, at Paris 

 the minimum oscillation was observed to take place in summer, 

 whilst, by Professor Forbes's deductions, it occurred in winter. 

 The results now under discussion give the minimum also in 

 summer, but the maximum in winter. We require, therefore, 

 a very accurate series of observations continued hourly for a 

 long time, in order to reconcile such discrepancies, and bring 

 us fairly acquainted with the course and nature of these atmo- 

 spheric tides. 



It may not be uninteresting, in concluding for the present 

 this part of the discussion, to tabulate a few of the best 

 authenticated observations of the barometric oscillations in 

 different parts of Great Britain. 



Table XVI. 



Place. 



Altitude 



above Sea 



in feet. 



Lat. 



N. 



Horary Oscillations 



Mean Oscillation 



Morning — 



Evening + 



Night - 



as deduced from 

 the Two - Oscil- 

 lations. 



10 A.M. 

 to 4 P.M. 



4 P.M. 

 to 9, 10 ,11P.M. 



9, 10, 11 P.M. 

 to 4 A.M. 



Plymouth 

 London ... 



York 



Edinburgh 



n 



95 



35 



430 



50-21 

 50-51 

 53-56 

 55-55 



-0166 

 •0280 

 -0174 

 •0106 



•0204 

 •0230 

 •0170 

 •0097 



•0171 

 •0166 

 •0094 



•0168 

 •0220 

 •0134 



The mean oscillation deduced from London in the above table 

 will, I apprehend, upon the whole, be found too great, owing 

 possibly to the want of a sufficient number of observations, 

 especially at 4 and 10 a.m. If we substitute for it Professor 



