256 Proceedings of the Royal Society. 
sented either by the square or by the cube of the square root of 
the density, the astronomical refraction may be obtained in a finite 
equation ; and having adverted to Mr. Ivory’s computation of the 
refraction with the assistance of converging series, and several trans- 
formations from an equation which expresses the pressure in terms 
of the density, and of its square, Dr. Young proceeds to observe, 
that if we substitute for the simple density the cube of its square 
root, we shall represent the constitution of the most important part 
of the atmosphere with equal accuracy, although this expression 
supposes the total height somewhat smaller than’ the truth; and 
that we shall thus obtain a direct equation for the refraction which 
agrees very nearly with Mr. Ivory’s table, and still more accurately 
with that in the Nautical Almanac, and with the French tables. 
At the horizon the refraction is equal to 33’ 49".5, which is only 
1.5” less than the quantity assigned by the French tables and in 
the Nautical Almanac, while Mr. Ivory makes it 34 17".5. Again, 
for the altitude 5° 44’ 21” we obtain 8’ 49.5 for the refraction, 
while the Nautical Almanac gives us 8’ 53”, and Mr. Ivory’s tables 
8’ 49".6. The author, however, observes that there is no reason 
for proceeding to compute a new table by this form u, since the 
method employed for that in the Nautical Almanac is, in all com- 
mon cases, more compendious; and even if it were desired to re- 
present Mr. Ivory’s table by the approximation there employed, we 
might obtain the same results with an error scarcely exceeding a 
single second, from an equation of the same form. 
Thursday, Feb. 5, and Thursday, Feb. 12. 
At these Meetings 
The Baxertan Lecturzr—On certain Motions produced in Fluid 
Conductors, when transmitting the Electric Current. By J. F. 
W. Herschel, Esq., F.R.S., was read. 
In the first paragraphs of this lecture Mr. H. particularly de- 
scribes the phenomena that result on placing a portion of mercury, 
covered with sulphuric acid, between the voltaic poles immersed 
on opposite sides of the globule of metal, but in contact with the 
