16 REPORT—1846., 
nient mode of determining the multiplier of %. But the multiplier varies rapidly 
with variations of « — 6; more slowly with variations of « + 6. Hence it would be 
convenient that a table should be arranged for small intervals of « —@ (say 1°, or be- 
low 1° to 15!), while larger intervals for « might suffice, as 5°. Hence this might be 
the form of the Table (or rather these the numbers to be calculated :— 
And for intermediate values, the multipliers would be given by interpolation. But since 
the result depends so much upon the value of « — 8, it would be desirable to observe «— 6 
directly, rather than by taking the difference of two observations. This may be done 
thus: take a dark cup full of water, and place it so that the surface of the water in it 
is seen at the cloud-point reflected in the lake. Also place it so that the boundary of 
the water in the cup when it falls upon the cloud-speck is in the vertical plane passing 
through the speck. Then the horizontal edge of the cloud-speck, seen in the lake andin 
the water-cup, will be dislocated, and the amount of dislocation subtends the anglea—f 
at the eye. Hence a— may be measured directly on the limb of the quadrant; or a 
micrometer affixed to the alidade of the quadrant for the purpose of measuring 2—8 
may easily be devised. The same formula and process may obviously be applied to 
measure the height of a mountain when h is known. If the height of the mountain 
be known, # may be deduced by the same formula. Without knowing 4, the formula 
will serve for comparing the height of a cloud with that of a mountain, when both can 
be seen in the lake. The arc a— will usually be very small, and will vary as its 
sine ; and in this case a+ will be 2« nearly. Hence, in comparing clouds and moun- 
sin2 « 
a— p 
seen very near the mountain top are inversely as the dislocations in reflexion. If the 
mountain image be dislocated three times as much.as the cloud-image, the cloud is 
three times as high as the mountain. If the altitude be different—for example, if the 
mountain be 15° and the cloud 45° elevated, and the dislocation still as 8 and 1, the 
height of the cloud is six times the height of the mountain (for, sin 2x 15°=%, 
sin2x45°=1). The same is the case of different strata of clouds. When seen in 
the same quarter, their heights are inversely as the dislocation of their images.—N.B. 
Perhaps a piece of glass ruled with parallel equidistant lines held at a given distance 
from the eye would be a good way of comparing dislocations of images. 
tains, their height will be as Hence the heights of a mountain and of a cloud 
On the Force of Vapour. By Captain SHorTREDE. 
The author adopts the experiments of the French Academy at high temperatures, 
and those of Magnus at low temperatures, as being the most carefully performed 
and the most extensive of all yet available. In the Academy’s experiments, the in- 
dications of the smaller thermometer in the steam are preferred to those of the larger 
thermometer in the water; because the temperature of the water increases with its 
depth, and always exceeds that of steam formed at its surface, besides the heat 
which may be necessary to overcome the cohesion of water in passing into vapour. 
