176 Mr J. D. FORBES on the Horary Oscillations 



made in the Temperate Zone, I rarely find any change made 

 upon them *. The table given in Sect. 1 has therefore been my 

 guide, as far as absolutely observed results are there given ; and 

 it would be unjust not to add here, that M. BOUVARD deserves 

 the thanks of all who take an interest in the subject, for the 

 spirited and valuable paper from which the table is extracted, 

 and for the unpublished or scattered results which he has there 

 combined, as well as that his particular theory is proposed with 

 much diffidence. 



As my investigation extends merely to the law of diminution 

 connected with latitude, I have confined myself to observations 

 near the level of the sea. The greatest exception is the result 

 of M. RAMOND at Clermont-Ferrand, at the height of 410 metres ; 

 but the excellence of the observations is such, and they agree so 

 well with those in the same parallel, that I could not omit them. 

 I have added the value given by Captain Sir EDWARD PARRY'S 

 observations for Port Bowen, and my own for the neighbourhood 

 of Edinburgh. My object being to determine the law of varia- 

 tion with latitude which should best represent a given number 

 of trust- worthy observations of the horary oscillation, I have em- 

 ployed a mode of investigation similar to that used by Mr AT- 

 KINSON, in his analysis of the law of mean temperature, forming 



* The principal deviation which I have remarked is in the extensive series of 

 M. MARQUE VICTOR, at Toulouse, where the observations were made many times 

 a-day, and probably had M. BOUVARD'S formula of reduction for hours applied to it. 

 However, it seems rather unaccountable how any formula of this kind should dimi- 

 nish instead of increase the amount of oscillation, which it actually does in this case, 

 unless there be some numerical mistake, the amount derived by M. MARQUE VIC- 

 TOR (and which I have verified as far as the combination of the annual means is con- 

 cerned) being l mm .20; according to M. BOCVARD it is l mm .OO. As, however, M. BOU- 

 VARD treats this as the best determined point in Europe, it is probable that he had 

 carefully examined the tables in the Memoires de T 'Academic de Toulouse, the later 

 volumes of which I have not been fortunate enough to see. 



