When one course of overlap disc-layering has been finished in the way described, I would advise you, this being your first experience, to lay your work aside and let it dry. It will be easy now to see whether the overlap adhesion by all that was desired, and what the process is capable of. You are to remember, please, that we aim at no mere sticking together comparable to the result of gumming or pasting, but to an actual incorporation of material, so that junction being once effected, the layers can never more be separated by any known means. Were it otherwise, a thick material resulting from aggregated sheets of paper would have no claim to the designation ‘artificial wood.’ It would be simply papier-maché, reducible to paper pulp by mere steeping in water; whereas the material you and I are now engaged upon may be not only steeped in water, but actually boiled, and will never come to pieces. It will behave under those circumstances exactly like natural wood—that is to say, will soften a little to a certain depth, no more.
Cupro-ammonium is a very funny thing to work with, and has many curious ways. One curious point is this: Capable of effecting such complete adhesion—nay, more, incorporation, actual, bodily, as we have seen it to be—yet that quality ceases after only a few minutes’ removal from the bath. If you ask me the why and wherefore, frankly, I am unable to tell you, not myself knowing, though I have worked at this material for more than twenty years. So whatever work has to be done with cupro-ammonium has to be quickly done.
Another point of very highest importance is the following: Do you remember my telling you not to be sparing in the quantity of cupro-ammonium poured from the ‘brewing bottle,’ as we will call it, into the dipping basin? The fact is that every bit of paper you immerse and withdraw weakens the original solvent power of the bath, so in proportion as the bath liquor is smaller in quantity, by so much more speedily will its working power be lessened. For a long time that working power can be, and in practice is, restored by additional copper steepage, but it cannot be restored indefinitely.
Now pour back your bath-liquor; put away your tools, hereafter to renew your bottle building. Go on adding layer to layer until your bottle is as thick as you wish it to be, then giving the thing a sharp crack with the hammer, the glass flask will crumble almost to sand, which, when shook out, your own flask of cuproxylene, or artificial wood, will remain without support, but quite able to take care of itself.
CHAPTER XXXIX.—How to Make an Astronomical Telescope.
BY FRANK CHASEMORE.
The investigation of astronomical phenomena can only be made with the aid of a good telescope, the purchase of which is attended with considerable cost. It is my purpose in this chapter to give such directions as will enable any boy with average ingenuity to make for himself, at the cost of a few shillings, an instrument with which he can observe the more interesting of these phenomena.
This telescope will be of the simple non-achromatic class—that is, the colour effect of the unequal refraction of light is not corrected. Object-glasses of the achromatic construction are very expensive. All refracting telescopes were of the simple class up to 1758, when Mr. John Dollond, who had a few years before set up in business in London as optician, discovered a way to correct the colour effect on the image. This was by making the object-glass compound, or of two or more lenses fitted to each other, each being made of a different quality of glass from the other and having a different refracting power, one lens correcting or neutralising the dispersing caused by the other. The lenses for our telescope can be had from Messrs. Dollond and Co., descendants of the above John Dollond, No. 1, Ludgate Hill, who have given me some valuable hints with regard to the construction of this telescope.
A refracting telescope consists of an eye-piece, a tube, and an object-glass; these are mounted on a firm stand. The object-glass at one end of the tube collects the rays of light, reflected from an object, to a point, in the focus of the eyepiece, which magnifies the image that is there formed, enabling the eye, placed at the orifice of the eyepiece, to see an enlarged image of the object.