VOL, 



LXX.] PHILOSOPHICAL TRANSACTIONS. 721 



would have found (supposing the observation to have been made as he says, on 

 the 4th day after new moon) that its perpendicular could not well be less than 

 between 11 and 12 miles. 



March 11, 1780, 7^- Promontorium Archerusia projected 17". 187- It is 

 very properly situated for measuring. By a proper deduction from the moon's 

 semidiameter, as given by the Nautical Almanac, at the time of observation, 

 we find the quantity on = 20.1 miles, and lm 22.6 miles; whence it appears, 

 that the perpendicular height of this mountain is a little less than a quarter 

 of a mile. 



Antitaurus, the mountain measured by Hevelius, was badly situated, because 

 Mount Moschus and its neighbouring hills cast a deep shadow, which may be 

 mistaken for the natural convexity of the moon. A good, full, but just mea- 

 sure, 25*. 105; in miles 29.27: therefore, lm 31.7 miles, and the perpendicular 

 height not quite half a mile. At 7^ 45"" this was repeated, in 2 different obser- 

 vations: a narrow measure 21 ".562; quite full enough 24''''.o62. These measures 

 give the perpendicular height less than half a mile. At 8*^ measured Lipulus, 

 l()".o63. It is also badly situated, though rather better than Antitaurus. Find- 

 ing that the projection increased, therefore concluded that this was not the 

 highest part of the mountain, and waited some time when he measured it again, 

 viz. at 9*'. Lipulus now projected 28*.75. Again at lO'' it measured 28".75: 

 this gives on = 33.64 miles. Distance of sun and moon about 63° 23': there- 

 fore LM 37.54 miles. Hence the perpendicular height is .64 mile, or very near 

 two-thirds of a mile. 



March 12, 1780, 7*^ one of the Appennine mountains between Lacus Tra- 

 simenus and Pontus Euxin us projected 44".o62. This gives us o« = 1.511 miles; 

 and LM = 52.9 miles: therefore the perpendicular height of these mountains, 

 which are very high, comes out to be I J- mile. 



Mons Armenia, near Taurus, projected 3l".4o6 = 36.43 miles; lm = 38 

 miles nearly, and the height f of a mile. Mons Leucopetra 34".4l79 or 40 

 miles; lm = 41.4 miles, and the perpendicular height 4 of a mile. 



March 16, lO"^ 30"^ Mons Lacer projected 4 5 ".625 ; but Mr. H. was almost 

 certain that there are 2 very considerable cavities or places where the ground 

 descends below the level of the convexity, just before these mountains; so that 

 these measures must of course be a good deal too large: but supposing them to 

 be just, it follows, that oh is 50. 193 m.iles, lm =: 64 miles, and the perpendicular 

 height above If miles. Another of the same mountains situated on the borders 

 of S. Sirbonis measured 41 ".87 5. This ridge of mountains is the same of 

 which he measured one on Jan. 17, which was then found to be 1.47 miles high. 

 Memoranda showing the matmer in which Mr. Herschel made his observa- 

 tions. — In fig. 7 , the points l, s, e, r, are all supposed to be in one plane: and 



VOL. XIV. 4 Z 



