256 Mr. Baily on an [Oct. 



the sun was still very considerable ; and that although some 

 places that were shaded from his light appeared gloomy, yet that 

 the day-light was not greatly obscured." He adds, that many 

 persons, about the middle of the annular appearance, although 

 not short-sighted, were unable to discover the moon upon the 

 sun when they looked without a smoked or coloured glass.* 

 Nevertheless Venus and some other stars were visible at the 

 same time ; and Venus continued visible even after the annulus 

 was dissolved. Venus was also seen in the eclipse of 1748, but 

 it does not appear that any other star was then visible. 



If the diminution of light should be considerable (which there 

 is not much reason however to suspect, - !-) Mercury, Venus, and 

 Mars, together with some of the principal fixed stars, may be 

 visible to the naked eye. Mercury, if visible, will be seen about 

 18° to westward of the sun, nearly in conjunction with liegulus: 

 Venus will be about 41° to westward of the sun : J and Mars 

 about 35° to eastward of the sun, not far from Spica Virginis, 

 The observer should also look out for any comet which may be 

 visible during this eclipse ; and be prepared to measure its dis- 

 tance from the sun or a principal fixed star. 



As many persons may be so situated as not to be able to pro- 

 cure any dark-coloured glass, for the purpose of viewing the 

 sun, I shall conclude this memoir by inserting Dr. Maskelyne's 

 method of smoking glasses, which he published in the Nautical 

 Almanac for 1769, in his Instructions relative to the Observation 

 of the Transit of the Planet Venus over the Sim's Disc in that 

 year. 



" Dark glasses should be used to defend the eye from the 

 intensity of the sun's light. Transparent glasses, smoked over 

 the flame of a candle or lamp, will give a more distinct and 

 agreeable vision of the disc of the sun than any tinged or 

 coloured glasses will do. Provide two pieces of glass of conve- 

 nient length, not too thick (the common crown glass, used for 

 windows, will do as well as any), wipe them clean and diy. 



* M. Le Monnier mentions the same thing of himself in the eclipse of 1748. 



+ In the annular eclipse of 1764 an ignorant country clergyman alarmed the 

 people of France by announcing that there would be total darkness during the 

 existence of the annulus; and the Rosal Academy of Sciences at Paris thought 

 proper to give this report a formal contradiction. It is well known, however, that 

 the smallest ray of light from tiie sun would prevent such a phenomenon ; as I have 

 shown more at length in n ( y paper "On the Solnr Lclipse which is said to have 

 been predicted by Thales," inserted in the Phil. Trans, for 1811, part ii. p. 220. — 

 I shall here take the opportunity of enrrectiuga typographical error in that paper; 

 where, in p;ige 240, line 22, " three degrees " should be " three minutes." Since the 

 publication of that paper, I find that the Bureau des Longitudes in France have 

 printed a Supplement to i\!. Burgh's Lunar Tables, wherein the mean epoch and 

 mean motion of the Supplement of the Node are considerably altered: so as to 

 bring the latitude of the moon within the limits which I there suggested. 



J In the total eclipse of 1715, Venus was seen when only nine digits were 

 eclipsed : but she was not seen at Compiegne in the eclipse of 1748, although the 

 digits eclipsed were 9j : in the eclipse of 1724, however, she was distinctly visible 

 when only six digits were eclipsed. This is not remarkable, as she is, in some 

 situations, visible even at mid-day. 



