1815.] Scientific Intelligence. 467 



visible in the day-time. But this reasoning will not apply to the 

 fixed stars ; since no telescope is found to augment their apparent 

 size, so as to make them resemble planetary disks. I am aware that 

 it may be said, that the telescope excludes almost all the light 

 except what comes from the object, and thereby prevents the im- 

 pression made by its light from being effaced ; and that by increasing 

 the magnifying power the ground upon which it is seen becomes 

 darker, forming a greater contrast to the light of the star. That the 

 first of these considerations, however, is not suiBcient to account 

 for the effect, I am pretty much convinced by the following experi- 

 ment. 1 have frequently directed a long tube, blackened in the 

 inside, and furnisiied with proper apertures to exclude the extraneous 

 light, to a star, about sun-set, when it was easily seen with a very 

 small degree of magnifying power, but could never perceive it 

 through the tube, though I was perfectly certain it was pointed 

 directly to the star. This experiment has uniformly failed of suc- 

 cess in detecting a star till it becanie visible to the naked eye. That 

 the darkness of the ground on which a star is seen is not, of itself, 

 sufficient to account for f lie effect produced by magnifying power, is 

 also evident from the following circumstance, viz. that by diminish- 

 ing the aperture of the object glass we may produce as dark a 

 ground as we please; but this contraction of aperture will not pro- 

 duce the effect of rendering a star visible if a small power be 

 applied ; nay, by diminishing the aperture beyond a certain limit, 

 we prevent a star from being seen, which would otherwise be ouite 

 perceptible, I am therefore induced to conclude that some addi- 

 tional reasons must be assigned why magnifying power produces this 

 effect. To ascertain these reasons is the object of this query. 



For similar reasons, I should wish to be informed if the fact is 

 established beyond all doubt that the stars are visible in the day-time 

 from a deep well or pit. This fact is generally taken for granted, 

 both by philosophers and by the vulgar, and has been asserted by 

 many rcspectaljle writers, both ancient and modern ; but none of 

 those whose works 1 have perused assert that they thoinselves, or 

 any of their learned friends, have witnessed this phenomenon. Otto 

 Gucricke, without questioning the fact, attempts to account for it 

 in the following manner : " It is," says he, " because the light 

 which proceeds from the stajs is not overpowered by the rays of the 

 Sun, which are lost in the number of reflections which they must 

 undergo in the pit, so that they can never reach the eye of a spec- 

 tator at the bottom of it." But for the same reason they ought to 

 be visible through a long tube, where the rays of light arc prevented 

 from striking the inside, by tlie interposition of |iroper apertures, 

 and more especially when such a tube is accurately directed to u 

 particular star, which is contrary to many ex[)eriinenlM \ have made 

 to ascertain this fact. Have any of your iiuin< r<nis philosophical 

 readers, or their friends, seen the stars from a deep pit in the day- 

 time ? Are colliers, miners, or subterraneous survi yurs, who are 

 frcf^uently in favourable i»ituatiyns for this purpose, known to have 



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