1817.] ^fr. Lofft on the 



After the greatest obscuration, tliere 

 was a hazy ill-defined darkness, extend- 

 ing very little from both cusps of tbc 

 Moon, particularly the left from the 

 observer, or eastern of the Moon : this 

 sceros from an atmosphere. It was of 

 perhaps 10 or 12". 



The Moon in general appeared, from 

 the ben:innitip; to the end of the eclipse, 

 perfec'.iy well defined; and especially 

 the limb in apparent intersection with 

 the O's disc. I looked for the volcanic 

 spot, but the Moon appeared nearly uni- 

 formly dark. At the time of the greatest 

 oBscuration, the phase was nearly as of a 

 Moon of about three days old. 



During part of the eclipse, an achro- 

 jnatic of Air. Nicholson's, editor of the 

 Pldlosophical Journal, was used — a very 

 •xcelleut instrument, now Mr. Acton's. 



The Iwiar parallax produced some 

 striking and curious changes in the an- 

 ffle of position of the Moon, seen on the 

 Suns disc, during this eclipse. 



I looked in vain for tiie very bright 

 star, Spica, then nearly on the meridian, 

 with an altitude of about 30°, during the 

 greatest obscuration ; the thertnonieter 

 was then 34° nearly ; at 7h. 20' it had 

 been 385; after the total emersion 41. 

 The dilfcrenee may be estimated at 6 or 

 8°, compared with its probable degree 

 of rise, had there been no eclipse. Had 

 it not been for the passage of the rays 

 from the Sun, w hich had quitted it pre- 

 vious to the greatest obscuration, the di- 

 minution, both of light and of heat, 

 would have been much gieater. 



The heavens seemed to favour observers. 

 From April 1, 1764, Ihe fine annular 

 eclipse, 1 do not recollect three eclipses, 

 a good observation of « hich has not been 

 rendered impracticable by the weather ; 

 I remt mber that, when a school-boy, as 

 a very fine dny. After the heavy rains 

 of the I8th, the day was fine till after 

 the ecliiise, and then cloudy. Not a 

 moment was lost by clouds interfering, 

 while the eclipse continued. 



Some observers have said, if the 

 Moon had any atmosphere, her penumbra 

 might have been seen on the Suns disc; 

 and so it might if the Sun's light were 

 by reflection, as the Moon's is. The 

 only place where indi<ations of atmos- 

 phere could have been expected, must 

 have been at the point of intersection ; 

 ■where the curves of the two discs came 

 in apparent contact; and f/i«t that such 

 au appearance did exist, I judge from 

 two telescopes — it was of very small 

 extent. But an atmosphere, had it 

 l>«eu cveu of 40 niiles, being only about 



late Solar Eclipse. <i99 



■5^ of the lunar diameter, would have 

 subtended an angle of only about 40" ; 

 and only the most dense part of it could 

 at all appear. But, where there is a 

 volci'im, it is pretty sure there must bo 

 an at:nospliere. 



The extreme evenness of tho limb of 

 the Moon, mountainous as she is, may 

 be well understood, for a reason long 

 since assigned; mountains whose ridges 

 lie between and against eacii other, so 

 as tp fill intervals, will, at a great dis- 

 tance, appear as a straight line. 



I wonder some optician did not think 

 it a good speculation to construct Sun- 

 glasses for the observation of tlii- late 

 eclipse. Mr. Benjamin ^Tartin did so 

 for that of 1764, — t!ie beautiful annular 

 eclipse; and the sale even then was 

 great. His was a dense red Sun-glasg, 

 set as in (he centre of a backgammon- 

 man, of a!)0ut haif-a-erown diameter. 

 But they might i)e variously fitted up^ 

 with dark green glass, to give a pal» 

 green image; stiong yellow lor a li/rkt 

 yellow; deep violet for a purple; deep 

 violet and dark g-rtcii combined, for a 

 pure white image. 



All tlnse combinations give a very 

 pleasing image, and such as contrasts 

 well with the Solar Spots ; and they tako 

 off nearly the wlwie setisiblc heat. iVIada 

 tolerably laige, and set in a cup-lih.» 

 frame oibox or pear-wooA, stained black, 

 they would shut out the latfral rays; 

 and either be useful singly to observa 

 solar eclipses, or adapt themselves to 

 almost any telescope, as eye-glasses for 

 viewing tl e Solar Spots. 



Pale green, or the blue, glasses, wonld 

 serve the purpose of turning off the too 

 great light in viewing the phases of Mer- 

 cury and Venus, near their cmtjunctiont 

 and their greatest elongations. 



Perhaps some friend to optics and to 

 astronomy may regard this hint as wor- 

 thy of adoption, against the transit of 

 Mercury in 1817, and the solar eclipse, 

 of 1820 ; still greater liere than the lato 

 one, and for other interm< diate pur- 

 poses. Capel Lortr. 



Ipswich; Nov. 21. 



P. S. In my last, the whole ought to 

 stand thus: — 



h. ' " d. Ii. ' " 



T V. 8 16 12,eclip.beg. TrucT.=19 ao IG 12T.A«ti, 



Eud 10 IX* 42, tud of eclipse, 22 15 24 



10 a) .V, - - - 16 39 



!>nration - - - 2h. 13 30 

 Or, .iccordinir to Mr. 

 Acton's observiitioiis, 2 14 45. 



Read also, for " eclipsis minorf" eclipsis 

 mimii incepit, 



S S 3 2V 



