VOL. LIX.] PHILOSOPHICAL TRANSACTIONS. 65Q 



5h 37m 23», he found no sensible difference ; and the sun's north limb was then 

 distant from Venus's north limb 7 144- of the micrometer, = 5' 17".6. This 

 gives Venus's diameter 58''.6; and the least distance of centres 9' 5Q".7- Hence, 

 the true duration of the ingress should be 18™ 56'; but this being here con- 

 tracted 15', by parallax, is reduced to 18"" 41'. So that the first contact, strictly 

 so called, happened 14^"" before the impression was discovered; and the central 

 ingress was at 2^ 38" 5'. The nearest approach was nearly, he supposed, at 

 5^ 37"". 



After Venus was entered on the sun, Mr. W. viewed her attentively several 

 times, with a power of the great telescope which magnified 260 times, but could 

 perceive no such duskishness round her as he saw at the internal contact, nor 

 that imperfect light on her disk, especially near the centre, which Mr. Dunn 

 speaks of; neither could he discover any satellite. Soon after 6, the western 

 sky began to be overcast, so that for a considerable time before sun-set the sun 

 was hid. The latitude of the place is nearly 42° 25' n. and the difference of me- 

 ridians west from London about 4*' 44™. But this may be further ascertained by 

 the following emersions of Jupiter's satellites, which Mr. W. observed with the 

 2-feet reflector. 



Emersions of Jupiter's first satellite. 

 Apparent time. 

 1768 April 25.-9'' 13" 52' 1769 May 14.. lO'' 19" 7' 



May 18. .9 27 27 Aug. 23. . 7 31 50 



June 10. . 9 37 25 Emersion of y's second satellite. 



July 3. .9 45 54 June 7-' 9 1 15. 



XLyil. Of the different Quantities of Rain, which appear to fall, at different 

 Heights, over the same Spot of Ground. By fVm. Heberden, M. D., F. R. S. 

 p. 359. 



A comparison having been made between the quantity of rain, which fell in 

 two places in London, a'oout a mile distant from each other, it was found, that 

 the. rain in one of them constantly exceeded that in the other, not only every 

 month, but almost every time that it rained. The apparatus used in each of 

 them was very exact, both being made by the same artist; and on examining 

 every probable cause, this unexpected variation did not appear to be owing to any 

 mistake, but to the constant effect of some circumstance, which not being sup- 

 posed to be of any moment, had never been attended to. The rain-gage in 

 one of these places was fixed so high, as to rise above all the neighbouring 

 chimneys; the other was considerably below them; and there appeared reason 

 to believe, that the difference in the quantity of rain in these two places was 

 owing to this difference in the placing of the vessel in which it was received. A 

 funnel was therefore placed above the highest chimneys, and another on the 



4 p 2 



