TRANSACTIONS OF THE SECTIONS. 



45 



Mr. Broun then showed the insufficiency of M. Dove's method, by a discussion of 

 observations made at Makerstoun in Scotland in 1843-46. In the winter quarter it 

 was proved that, so far from the morning maximum disappearing, the diurnal varia- 

 tion of dry air pressure showed a better marked double oscillation than was exhibited 

 by the barometer. Further, it appeared that the amount of the diurnal oscillation of 

 the barometer had no relation whatever to the amount of diurnal oscillation of 

 vapour tension or of temperature ; the sum of the barometric diurnal oscillations at 

 Makerstoun being greatest when the amount of the diurnal variations of vapour 

 pressure and of temperature were least. It was also remarked that there were 

 secondary maxima of vapour pressure which did not show themselves at *ll in the 

 barometric results ; or that when the tension of vapour by the psychrorneter observa- 

 tions seemed to increase, the total pressure, as measured by the barometer, gave no 

 symptoms of it. 



M. Dove had brought forward as a proof of the accuracy of his method, the 

 statement that in places far in the interior of the Asiatic continent, such as Cathe- 

 rinenburg, Nertchinsk, &c, distant from large masses of water and with dry 

 atmospheres the double diurnal oscillation was not shown in the barometric observa- 

 tions. Mr. Broun pointed out that this should not depend upon the mean dryness 

 of the atmosphere, but upon the diurnal variation of vapour tension as computed by 

 the psychrorneter. He compared the diurnal variations of vapour tension at Nert- 

 chinsk and Makerstoun in 1844, which were as follows : — 



As the range is as great at one place as at the other, there can be no better reason 

 (as far as this point is concerned) for the barometric oscillation being single at 

 Nertchinsk than at Makerstoun. 



But in order to test the method more perfectly, one of the dryest months (January) 

 of the year 1844 was chosen ; in that month the diurnal variation of vapour tension 

 at Nertchinsk was between 0'008 in. at 6 a.m. and 0-017 in. at 1 p.m. The oscillations 

 were compared with those for the same month at Makerstoun in Scotland ; the 

 comparison will be best understood by the following Table : — 



Oscillations of Barometer and Dry Air Pressures at Nertchinsk 

 and Makerstoun, January 1844. 



It will be seen from this Table that the barometer diurnal oscillations at Nertchinsk, 

 in the interior of a great continent, for the month of January 1844, agreed within a 

 few thousandths of an inch with those for Makerstoun, a quite insular locality ; the 

 greatest difference being in the afternoon minimum, which falls 007 in- more at 

 Nertchinsk than at Makerstoun. The diurnal variation of dry air pressure shows a 

 distinct and well-marked double maximum and minimum like that at Makerstoun. 



Mr. Broun concluded his examination of the sufficiency of M. Dove's method, by 

 a discussion of observations made in the observatory of His Highness the Rajah of 

 Travancore atTrevandrum ; from which it appeared that the double diurnal maximum 

 and minimum of dry air pressure were shown in the dry quarter, that of land and 

 sea breezes ; in the monsoon quarter, that of continuous N.VV. winds ; and in the 

 means for the whole year ; but most distinctly and regularly in the monsoon quarter, 

 when no land and sea breezes are blowinjr. 



