reckoned from the south.
Hence the position of the sun is ascertained for both negatives.
By actual measurements on the plates and reference to a previously constructed scale the position of the cloud as seen from each camera is next determined, and the angle subtended by the base line at a point X vertically beneath the cloud is calculated. If A and B are the stations, and a and b the angles from them respectively, the distance AX is given thus—
log AX = L sin b-L sin AXB + log AB,
and the height h of the cloud above X is given by—
log h = log AX + L tan alt.-10.
Transcriber’s Note
Variations in hyphenation (i.e. thunderstorm and thunder-storm) have been retained. The following apparent typographical errors were corrected:
Page [171], “focussed” changed to “focused.” (it should be focused on the horizon)
Page [173], “aperature” changed to “aperture.” (the lens with its large aperture)