ee eT 
ON THE ELUCIDATION OF METEOROLOGICAL PHENOMENA. 1738 
The site, moreover, admits of the selection of a base-line lying exactly 
east and west, a point of some importance for simplifying the reduction of 
the observations. 
The observing stations are at present placed only 200 yards apart. 
They are connected by a line of wire stretched on small telegraph poles in 
the ordinary manner. At each end the iron wire is soldered to an india- 
rubber coated insulated copper wire, which is led down one of the stays of 
the last pole into the camera-stand, in such a manner as to prevent any 
rain-water from flowing down this wire into the apparatus contained in 
the stand. 
Each stand is a four-sided cupboard built of thick matchboarding, 
three sides sloping towards the top, which forms a level table about 
18 inches square. The fourth side, which faces north, contains a door 
which can be locked. The base of the cupboard is about 2 feet 6 inches 
square, and is supported by four legs about 9 inches above the surface of 
the ground. Several coats of paint have made these stands so secure 
against weather that exposure for more than two years has not effected 
any injury except a slight shrinkage in the top, which is easily repaired. 
As the cameras and electrical apparatus are contained in these boxes, their 
construction is important. 
The two observing cameras have been specially constructed. Each 
swings on trunnions between uprights rigidly secured to a flat stand. The 
camera can thus be directed to any altitude, and can be firmly clamped. 
In order to make this clamping secure, und at the same time add to the 
steadiness of the whole, there is fixed to the base board of the swinging 
camera a flat board whose margin forms a segment of a circle whose centre 
is the same as that of the trunnions. This passes smoothly between two 
pieces of wood let into the flat stand, which can be drawn together by a 
screw, thereby grasping the margin of the circle. The surfaces of contact 
are faced with leather, in order to prevent any sticking or injury to the 
polished clamping-board. j 
_ Adjustment in azimuth, which need not be done with any great exact- 
ness, is effected by rotating the whole apparatus on the levelled top of the 
eamera-box. Each camera is provided with a lens of 18 inches focal 
length, which is provided with an iris diaphragm, and covers a plate of 
the size known as whole plate. 
The two lenses were carefully compared, both by testing their focal 
lengths by the ordinary methods, and finally by comparing two views 
taken simultaneously with the two cameras placed side by side. When it 
was seen that the two pictures coincided exactly, it was certain that the 
adjustments were correct, and the focus of each camera was fixed by 
firmly screwing up the adjusting screws and putting a coat of varnish 
over them to prevent any possibility of after-slipping. This fine adjust- 
ment is rendered possible by making the back part of the camera of the 
well-known ‘bellows’ pattern. In order to be sure that no shrinkage of 
the materials should affect the result, they were made of old, well-seasoned » 
wood, were adjusted and freely exposed to sun and wind, and to the 
changes of temperature and moisture experienced by keeping them for 
several months in the camera-boxes. On again testing them by the 
superposition of two negatives, no change could be detected. The lenses 
are provided with shutters, which can be simultaneously released by an 
electro-magnet fixed to the front of the camera. The shutters used at 
present are of the kind known as the ‘chronolux,’ which can be adjusted 
