: 35-1- 'Mr. Smeaton’s Obfervation of Mercury 
Invejligatlon of the efj'&Bs of refraCtion. 
The preceding dedu&ions-and remarks v fhew the confifteney 
of the obfervations with themfelves ; yet, * from' the poii- 
tion of the telefcope, it being only elevated n°f above the 
horizon?, it is necelFary to examine how far the deductions 
above fpeeified were, capable of being affeCted by refraction. 
And in this refpeCt'it will appear, that if it be fuppofed, there 
-is no difference in the quantity ©f refraCtion of fuch objects as 
appear within the limits of the held of view of this inftrument 
(which is i° i y), then their relative pofitions to each other will 
not be affeCted thereby : for if in fig. i . (Tab. XIII.) we fuppofe 
the circle-X HRO to reprefent the boundary of the field of view, 
HO being an horizontal and VR a vertical line, each, paffing 
through, the ..center of the field at L; and if PLP denotes a 
part of a parallel of declination, then BLX perpendicular 
thereto, will be apart of an horary circle, both palfing through 
the fame center. Now let d* be the apparent path of a flar, 
fuppofing it unafFe&ed by refraCtion fill it comes to the vertical 
line at *, and there to be lifted' up by refraCtion in the faid 
vertical to L. Let e+ denote another ftar, alfo unaffeCted by 
refraCtion, to pafs along the .different parallel of declination 
e+ till it comes to + ; then, if it be fuppofed that the two 
'Itars are both fituated in the fame horary circle, if at the point 
+ refraCtion takes place, and by hypothefis • this is lifted up 
equally with ’the other, in the perpendicular +/, then the 
line +* being drawn through the places of the two Itars, will 
• be cotemporary and parallel to LX; and the figure /+ #L 
being evidently a rhomboides, the two Itars, fo altered by 
* .This will readily be deduced by infpedion of the celeftial globe. 
refraCtion, 
