2 ON THE REDUCTION OF THE 
No formula is given for use with Table XIX.’, but it is stated 
that the table may be employed “for reducing barometrical observa- 
tions to the level of the sea, and also to any other level by a similar 
process.” An example is, however, given, applying tables in French 
measure, corresponding to XIX.’, the method of which example may 
be represented by the formula 
V VW. *10’ (u1.) 
where NV, is the number in the table corresponding to the baro- 
B 
metric reading* and temperature at the upper station, and Pel + that 
corresponding to those at the lower station ; an approximate reduced 
barometric reading and temperature being employed in taking out 
the latter quantity. 
Formula (i.) may also be employed with Table XTX.’, 6 being any 
height and WV the number in the table corresponding to 6. No advan- 
tage is, however, gained, by using this table instead of Table XVI. 
with formula (i.), unless 6 be taken nearly equal to f, so that we 
may have, nearly 
Z 
k=yy' 
Laplace’s formula for computing differences of elevation from baro- 
metrical observations, from which each of the above is deduced, may 
be written 
B wa 
4-4 GB (11.) 
where A, is a constant, depending on the mean between the tem- 
peratures at the upper and lower stations. Strictly, it also depends 
upon the latitude of the station, and on the height above the sea; 
but the variations due to these may be neglected, unless the height 
is very considerable. 
Now the number oul ME in the above mentioned tables, for baro- 
meter reading 6, and temperature ¢, is the difference of elevation 
* Throughout this paper, when a barometric reading is spoken of, the reading reduced to 
temp. 32° Fahr. is to be understood, 
