340 
PROFESSOR O. REYNOLDS AND MR. W. H. MOORBY 
The Correction for g in Latitude of Greenwich and 45°. 
42. Since the latitude of Manchester is 53° 29', Greenwich 51° 29', the value of g 
being (“ Memoires sur le Pendule,” ‘ Soc. Francaise de Physique ’) 
•“ 0'00259 cos 2X) = g^^o (1 0 0007558) at Manchester, 
)> jj =1745°(1 + 0’0005814) at Greenwich, 
whence the correction factor is . . . . (1 + 0-0001746) for Greenwich, 
and for 45°.(1 + 0-0007558). 
The Specific Heat of the Water. 
The standard capacity for heat being that of distilled water, the obvious 
course would have been to have used distilled water in the trials, had this been 
practicable; but as it was apparent from the first that the quantity of water which 
would have to pass through the brakes during the trials would amount to some 
20,000 gallons, or, say, 100 tons, all of which -R^ould have to be brought down to a tem¬ 
perature of 32° Fahr.; and that to do this, using distilled water, whether or not the 
water was used over again, the necessary appliance for producing, storing and cooling 
the water, were impracticable in the laboratory, the last 40° must be removed with 
ice, and this would require some 25 or 30 tons of ice. While using the town’s water 
direct from the main, the average temperature, from February to June, wmuld not 
exceed 45 , so that only 12° or 13° would have to be removed by ice, which would 
require from 7 to 10 tons, with no other appliances except the relatively small 
appliance for cooling. 
The only practical course, therefore, was to use the town’s water. And had it not 
been for the known purity of this, the research would never have been undertaken. 
As affording definite assurance of the consistent purity of this water, as delivered 
in the college. Professor Dixon kindly undertook to furnish the mean results of the 
analyses which he makes periodically for the Manchester Corporation, of the water 
drawn from the supply in the college. These show that the impurities are almost 
negligible, taking 0-2 as the specific heat of the salts, the relative correction is 0 - 85 , 
where 5 is the relative weight of the salts. 
The Effect of Air in the Water. 
43. Even distilled water contains air unless special precautions are taken foi- its 
removal ; so that any effect such air may have on the capacity for heat as measured 
would not have been avoided by using distilled water. 
Ihe direct effect of the same 0-00323 per cent, of air which water exposed to the 
atmosphere usually contains at normal temperatures, is so small as to be altogether 
