176 H.F. Blanford — Ineq^^Mlity of semi-cliiirnal Barometric Tides. [August, 



insect Phyllocrcmia WesUvoodi notwithstanding that the prothorax has 

 no foHaceous expansions. 



Similar sexiial differences may be looked for in Fhyllocrania, Parabl- 

 pliaris, and Sibylla, the males of which are still vmknown. 



In the FJiasmidce, we meet with apparently similar sexual differences, 

 but in these insects the great reduction in size and thickness of body that 

 has taken place in the males may well have effaced the horns and foliaceous 

 lobes which after all are generally relatively not very greatly develojDed 

 in the females ; we see the truth of this in the cases of the genus Pliyllium, 

 wherein the foliaceous lobes of the abdomen and legs of the female are rela- 

 tively very large and those of the male are consequently by no means in- 

 appreciable, and in the case of LoncTiodes insignis, in which in males 

 more than ordinarily stout the cephalic horns reappear in rudiment though 

 they have disappeared in slenderer individuals. 



Mr. Wood-Mason also announced that he had ascertained by actual 

 observation of living specimens belonging to several species that the 

 femoral brushes described at a recent meeting are used by the JKantidce to 

 keej) their eyes in a functional condition ; and that they are present in the 

 young when they quit the Q%^. 



The following papers were read : — 

 1. On tlie 'pliysical explanation of tlie Ineqtiality of the two semi-diurnal. 



Oscillations of Barometric Pressure. — By H. F. BLANroED, Esq., 



F. G. S., Meteorological Beporter to tlie Govermnent of India. 



(Abstract.) 



Mr. Blaistoed said that the paper he had to bring before the meeting 

 dealt with a phenomenon which to observers in tropical countries is one of 

 the most familiar and most regular in the whole range of Meteorological 

 physics, but is, at the same time, one, on the explanation of which the 

 greatest diversity of opinion prevails. 



It needs but to observe the rise and fall of the barometer for a day or 

 two, in about any part of India, to learn the fundamental fact, that the 

 atmospheric j)ressure undergoes daily, a double oscillation which is so 

 regular in its occurrence, that except dming the passage of a cyclone it is 

 scarcely ever masked by the irregular or not periodic variations. From 

 between 3 and 4 in the morning the pressure begins to rise, slowly at first, 

 afterwards more rapidly, and it attains its maximum generally between 9 

 and 10 ; the exact hour varying at different seasons of the year. It then 

 falls with great rapidity during 3 or 4 hours after noon, and attains 

 the lowest pressure of the 24 hours about 4 or 5 p. m. Again a 



