720 PHILOSOPHICAL TRANSACTIONS. [aNNO 1 780. 



high mountain projected no less than 40".6'25. Its situation is in the south-east 

 quadrant. The moon's semidiameter, at the time of observation by the Nau- 

 tical Almanac, was \& 2". 6; therefore, — = 45 98 miles = on. 



Sun's longitude at 7^ 9' 27° 39' O" 



Moon's long, at 7 2 2 46 52 



Their nearest distance 4 5 7 52 



or about 125° 8'; the sine of which is .8104: thence we find lm 56.73 miles; 

 and the perpendicular height of the mountain is 1'".47., or less than a mile and 

 a half. 



Jan. 22, 8'^ 20' the highest mountain, situated near Snell or Petavius, pro- 

 jected 1 1".437, which is 12'.34; and lm comes out to be 35.3 mile: therefore 

 the perpendicular height is .57 mile. Another, just behind Mare Crisium, 

 measured only 7", therefore is less than half a mile high. 



Jan. 25, 7^ 30' in the morning, a mountain near Aristoteles measured 18".59, 

 which gives 20.6 miles; and lm is found 28.53 miles; the perpendicular height 

 is therefore only .37 mile. Other mountains about Mare Nectaris measured 

 about 23". 5; but they had hills before them, and their situation was not so 

 proper for the purpose. However, it is evident they were of no considerable 

 height. 



Jan. 28, 6 o'clock in tiie morning, the highest mountain in the disc measured 

 30".937; the moon's semidiameter at that time 15' 40"; and on therefore equal 

 31.37 miles; but as the moon is within 4 hours of her quadrature, we may be 

 assured that this mountain is less than half a mile high. 



Feb. 19, Mons Sinopium projected 5".781; therefore on = 6.26 miles, and 

 the quantity lm 36.54 miles; and consequently the height of this mountain, 

 which it seems proves to be a very high one, is not much less than a mile and a 

 half. However, the journal observes, that the measure was very full; therefore 

 the mountain in all probability does not exceed a mile and a quarter. Besides, 

 Mr. H. thinks that observations made so near the full or new moon are less to be 

 depended on, because a small error in measuring will produce a great one in the 

 height of a mountain. 



From these observations Mr. H. believes it is evident, that the height of the 

 lunar mountains in general has been greatly over-rated ; and that, when we have ex- 

 cepted a few, the generality do not exceed half a mile in their perpendicular 

 elevation. It is not easy to find any certain mountain exactly in the same 

 situation it has been measured in before; therefore some difference must be ex- 

 pected in these measures. Hitherto he had not had an opportunity of particularly 

 observing the 3 mountains mentioned by Hevclius; nor that which Ricciolus 

 found to project a l6th part of the moon's diameter. If Keill had calculated the 

 height of this last-mentioned hill according to the theorem Mr. H. has given, he 



