6 12 PHILOSOPHICAL TRANSACTIONS. [aNNO I762. 



and density) through which the rays then pass, being compared with the like total 

 depth and density thr(»ugh which they pass at several elevations, it was propor- 

 tionable to the difference of apparent magnitude, as appearing to the naked eye. 

 This circumstance of sudden increase and decrease of apparent magnitude, and as 

 sudden decrease and increase of light, (for they both go together) seemed no im- 

 probable cause of the phenomenon, though he could not then perceive how such 

 vapours might contribute toward enlarging the diameter of the sun apparently in 

 a horizontal direction. 



He therefore examined the sun's disk again and again, by the naked eye, and 

 bv telescopes, at different altitudes, and, among several circumstances, found the 

 solar maculae appear larger and plainer to the naked eye, and through a telescope, 

 the sun being near the horizon, than they had appeared the same days when 

 the sun was on the meridian, and to appearance more strongly defined, yet 

 obscured. 



Before sun-rising, when the sun has been near the tropic, and the sky at the ut 

 most extent of the horizon has appeared very clear, and when certain fogs have 

 appeared in strata placed alternately between the hills, and over intervening rivers, 

 valleys, &c. so as to admit a sight of the rising sun over those fogs, Mr. D. had 

 often observed, with admiration, the most distant trees and bushments, which at 

 other times have appeared small to the naked eye, but while the sun has been 

 passing along a little beneath the horizon, obliquely under them, just before sun- 

 rising, when the sun has beennhus approaching towards and beneath any trees 

 and bushments, they have grown apparently very large to the naked eye, and also 

 through the telescope ; and they have lost that apparent largeness as the sun has 

 been passed by them. Thus a few trees standing together on rising ground, at the 

 distance of a few miles, have appeared to grow up into an apparent mountain. 

 Such apparent mountains formed from trees, put on all forms and shapes, as 

 sloping, perpendicular, overleaning ; but soon recover their natural appearance, 

 when the sun is passed by them, or got above the horizon. 



Mountains themselves at a distance sometimes appear larger than at other 

 times. Beasts and cattle in the midst of, and being surrounded with water, 

 appear nearer tons than when no water surrounds them. Cattle, houses, trees, 

 all objects on the summit of a hill, when seen though a fog, and at a proper dis- 

 tance, appear enlarged. All bodies admit ot larger apparent magnitudes, when 

 seen through some mediums, than others. But more particularly, 



He took a Cylindrical glass vessel about 2 feet high, and having graduated its 

 sides to inches, he placed it upright on a table, with a piece of paper under the 

 bottom of the glass, on which paper were drawn parallel right lines, at a proper 

 distance from each other ; and having placed a shilling at the bottom of the ves- 



