THEEE QUESTIONS. . 73 



volatlon of the mirror. But when the eye is at a confiderable Small revolving 

 diftance, a fmall perfect image is feen, which when the diame- handed, 

 ter of concavity is horizontal, is ere6t but not left handed ; that 

 is to fay, if you move your right hand, the image alfo moves 

 its right hand, inftead of the left, as happens in a convex and 

 a plain mirror; when the diameter of concavity is vertical, the 

 image is inverted, but ftill right handed ; and in the other po- 

 rtions of the mirror it takes every poffible Situation of obli- 

 quity, making two complete revolutions for one of the mirror 

 itfelf. The image is larger the nearer the obje6t, and theerefl 

 image is a little broader than the inverted ; this deformity be- 

 ing more confiderable the larger the image. 



Now Sir, my fimple queftion is. Where is this image ? Is it Where is thit 

 before the mirror, according to the property of the convex, or i^behind the* 

 behind it, according to that of the concave. I thought to mirror, 

 have difcovered this by the folar focus, or by applying a mag- 

 nifier to the fmall image, but neither method anfwered my pur- 

 pofe, and nothing within the fmall extent of my knowledge 

 has enabled me to folve it by reafoning. 



3. The enlarged appearance of the moon near the horizon, Flatnefs of the 

 and the flat vault prefented by the concavity of the heavens, ^y a"d horizon* 

 have been explained by various allufions to the diminifiied light 

 after pafling through a portion of the atmofphere, and its di- 

 redion over a long row of objeds, fuch as trees, houfes, <fec. 

 Something feems to be wanting in thefe accounts. Neither tfee 

 fun or moon are ever fuppofed to be more diftant or larger when 

 feen at confiderable elevations through clouds or mifts ; and 

 the Iky feems flat, and thefe luminaries enlarged, whether the 

 profpe6l be over woods, lawns, naked plains, or the calm fea. 

 Befides which, I have no hefitation in infifting that the iky ap- Not the fame at 

 pears loftier on fome days than on others, and even at the fame ^^^ ^rtitiy &c* 

 inftant of time on difl^erent fides* If this be no error, w^hat 

 are the caufes of the appearance or the convidion produced in 

 our minds ? 



I am. Sir, 



Your obliged reader from the firft. 



R.B. 



I believe my correfpondent would have vanquilhed his dif- 

 ficulties, with a little more confideration. If the explanation 

 be not given by fome of my correfpondenls, I fliall endeavour 

 to give the replies he requefls in pur next. W. N. 



