VOL. LXXXIV.] PHILOSOPHICAL TRANSACTIONS. 423 



soon after the beginning of the eclipse three high ridges of mountains on the 

 south-east border of the moon projecting sensibly into the disc of the sun ; one 

 of them appearing to be a long and considerable mountainous range, and the 2 

 others to the westward being more in the shape of prominent points. This was 

 seen with the 7-feet reflector magnifying only 50 times, but this very distinctly : 



1 applied a power of l6o, together with the projection machine, and found that 

 the two last-mentioned points were from 24 to 28* asunder ; that the long eastern 

 range was somewhat more distant from the nearest of the former, and that all 

 of them projected, if not 4, at least 3" beyond the rim of the moon ; so that 

 their height from the said rim could not be less than 4 of a German mile. 



Soon after, when the south-western limb of the moon had advanced a little 

 farther on the disc of the sun, I discovered on this part another equally pro- 

 minent mountainous range, which I also measured and delineated. It consisted 

 of a ridge I'and from 30 to 40", and therefore not less than 23 or 24 geographical 

 miles in length ; and 4 insulated mountains to the westward, all projectino- from 



2 to 3" beyond the rim of the moon ; these I had little doubt must be parts of 

 the very lofty mountainous region Leibnitz, which a particular libration now 

 presented in such a projection to our sight. 



XIX. Experiments and Observations made with the Doubter of Electricity, ivith 

 a Fiew to determine its Real Utility, in the Investigation of the Electricity of 

 ^Atmospheric Air, in Different Degrees of Purity. By Mr. John Read, 

 p. 266. 



When I employ the doubler to investigate atmospheric electricity, I use it 

 with its revolving plate uninsulated, when opposite to that fixed plate which is 

 insulated ; because, with respect to insulation, that position of the doubler 

 exactly corresponds to the insulated and uninsulated parts of my high pointed 

 rod, and of course their electrical accumulation will always be of the same kind 

 in all weak electrifications of the atmosphere. 



Some observations, which 1 made some time ago, inducec* me to suspect that 

 air, by being vitiated even in a small degree in various ways, as by respiration, 

 putrefaction, &c. lost a portion of its natural electricity, and so became electri- 

 fied negatively : the following facts seem to substantiate this supposition. The 

 room I usually inhabit being of small dimensions, is on that account more liable 

 to suffer a change in the electrical state of its air than a larger one ; and having 

 been often struck with the constancy of the doubler charging negatively in it, 

 whereas in the open air, and often in the adjoining room, which is larger, the 

 doubler would give positive electricity ; I saw nothing to occasion this difference 

 between the two rooms besides what could be attributed to the respiration and to 

 the usual effluvium of my body. I was therefore curious to try on the 9th of 



