200 On Refraction. 
particular time. As the scale of the barometer bears examina- 
tion, and as the formula (Dr. Maskelyne’s) will scarcely be ques- 
tioned, it is only in the specific gravity of the mercury, or in an 
erroneous estimate of the proportion of the area of the tube to 
that of the cistern (};), that we can louk for the uniform disere- 
pancies. 
Comparison of the Altitudes given in the Trigonometrical Sur- 
vey and in the present List (reduced ta the ground). 
Table. Trig. Survey. Diff. 
Ingleborough es »» + 2368~ 2361 (walsh? 
Pennigent av a 2281 2270. wn sihl 
Great Whernside , ti 2309 2263 .. 46 
Rumbles Moor oe ee 1318 1308... 10 
Pendle oe : ee 1824 1796....- 28 
Bodlaworth «. Q& Bie Gt 1692 ° s AGS9,ofaiene ss 
The differences are in general very trivial; and may we not 
assign as a reason for the two marked exceptions, that the great 
theodolite was not used either at Pendle Hill or at Great Whern- 
side, and that the refractions made use of in the calculations 
were greater than the reciprocal observations in the vicinity could 
warrant ? .. 
All the angular instruments employed in these operations were 
made and divided by the late Mr. James Allan. 
{ The author is respectfully informed, should the Journal 
of the Thermometric Indications at the summit and base of. 
Rumbles Moor, which he states has been kept from the beginning 
of February, and will be discontinued on the Ist of April, present 
any interesting results, that I shall be happy to make room for it 
in the pages of the Phil. Mag. and Journal.—A. T. 
_XLY. On Refraction. By Josrpa Reapr, M.D. 
[Continued from yol. lviii. p. 254.] 
Is my last communication J mentioned a simple, and I hope, in 
the opinion of men of science, a conclusive experiment against 
the commonly received doctrines of refraction. I shall now men- 
tion the following variation. Having procured a very clean cy- 
lindrical tumbler (fig. 7, Plate III.) with a flat bottom, about 
three inches diameter, I placed half-a-crown at the bottom, and 
holding it near a well lighted window, I poured in water by very 
small quantities at a time, my eye. being on a plane: as soon as 
the object was entirely covered, a reflected image formed imme- 
diately over it, which rose with every addition of water: having 
poured 
