M. A. AINSLEY
In deciding on the mounting to be adopted for the 9 in. telescope, I was guided principally by consideration of expense and of the possibility, or otherwise, of getting the work done. Not having any workshop, I was unable to do the work myself and had to rely on the ability and intelligence of the local blacksmith and carpenter. The result is a mounting which is rough and might be much improved; but it has proved efficient and steady and most convenient in use. It is not, however, so well suited to the longer focus of the second mirror, or indeed to any focus of more than 6 ft. The mounting has proved especially convenient for sweeping up comets, nebulae or planets in daylight, on account of the ease of motion in any direction. I do not propose to give drawings of it, as any of my readers who are building a telescope will probably modify the arrangement to suit their own preference ; but the accompanying view will show how the whole thing was arranged.
It will be seen from the photo that the slow and rapid motion in altitude is obtained by means of a windlass and a wire cord passing over two pulleys. There being three lines of wire, the motion of the telescope is reduced in this proportion. This arrangement was found to allow of very rapid motion in altitude when required; or the motion could be made slow enough to keep a star central in the field of view with a power of 480. I used bronze picture wire, which worked well, but was Jiable to fray. I think the steel wire used for Bowden brakes would be better; but it should be galvanized or well greased. The larger the pulleys are, the better the arrangement will work; those shown in photo are undoubtedly too small. The pulleys used for the weights of an old-fashioned grandfather's clock are very suitable.
It will be seen that the telescope is carried on two points of iron on one side of a square platform of teak 2 in. thick. This is bolted to a 6 in. plate of iron which is, in its turn, carried on a vertical 2 in. shaft about 20 in. long. The bearings for the vertical shaft are two iron plates at the ends of a stout wooden tube about 5 in. square, which, in my case, is supported vertically on an iron framework. A stout wooden tripod would be just as good; but it should be made as heavy as possible to avoid all danger of capsizing in a wind. At the sides of the square platform will be seen two long teak beams which carry the bearings for a 1/2 in. iron axle with a handle at one end. This forms the elevating windlass; while the lower pulley is screwed to a crosspiece underneath the axle of the windlass.
The points on which the tube is supported are fixed so as to be half the diameter of the tube above the c. g. thereof. This insures.that the mirror end always has a tendency to fall, and keeps the wire taut; the friction of the windlass prevents the tube moving, and this is adjusted by screwing down the caps of the bearings. It will be found that with foci up to 6 ft. the handle comes conveniently for the left hand; with, longer foci it would probably be better to put the windlass on the lower side of the tube itself.
Quick motion in azimuth presents no difficulty, the telescope turning easily about the vertical axis; but the slow motion gave some trouble, as 1 was unable to go to the expense of tangent screws, universal joints, etc. The arrangement finally adopted has proved effi-cient, but requires a little practice to work.
A hole is bored in the near side of the teak square, and the end A, Fig. 2, of a long screw is inserted, there being a hinge, to enable the screw to lie in any direction. On the screw works a brass wheel about 6 in. diameter, which bears against the end of a galvanized iron gas pipe about 3 ft. long. The lower end of the gas pipe bears on the ground. For quick motion the gas pipe is raised off the ground; when the object is in the finder is placed somewhat to the left of the center of the field of view, and the gaspipe allowed to rest on the ground, the brass wheel being then turned the telccopeis pushed slowly round until the object is central in the field, when it is followed by turning the brass wheel. It will be seen that the slow motion only acts one way - i. e., it only turns the telescope to the right. This is undoubtedly a defect; but as nine objects out of ten, including sun, moon and planets, have their apparent motion in that direction, little inconvenience is caused after one is accustomed to the working. Anyone with mechanical skill and ingenuity will doubtless be able to improve on the arrangement. If the focus is longer than 6 ft. it will perhaps be found difficult to reach the wheel with the right hand; but there is no reason why the pipe should not be made longer, and a post fitted to the teak square to raise the wheel higher.
On commencing the work the gaspipe is turned so as to come under the end of the tube. The tube is then placed on the mounting, the point supporting it falling into two shallow holes in the platform; the mirror end is then allowed to rest on the pipe and the windlass unwound, and the wire and pulley hooked on; and on finishing, the windlass is wound nearly home, the wire unhooked and the tube carried indoors.
Of course the dimensions and details of the mounting can be altered at will to suit varying conditions. Though rough, the mounting has proved very efficient and steady in my hands, though I do not claim that it is by any means perfect.
A great number of processes have been published, and all are good; but I strongly recommend a trial of the formalin process. When once mastered it is so quick and convenient that its slight uncertainty may be put up with. Experiments may be made on small pieces of glass until the right pro-proportions of the various ingredients are determined. The chemicals required are: 10 per cent solution of nitrate of silver, 10 percent solution of strong liquid ammonia; commercial formalin (40 per cent formaldehyde). The above must be made with distilled water. Saturated solution of potassium bichromate, to which strong sulphuric acid has been added in the proportion of about one oz. to the pint; a small quantity of absolute alcohol; 2 gal., or more, of distilled water.