A. Chill plate of cast iron turned to the curve of the speculum B. Turned hoop of wrought iron with opening at O. C. Pouring pocket. D. Counterpoise, By which the chill plate is tilted up The largest figure in the engraving is the annealing tub of cast iron filled with sawdust, where the speculum is placed to cool as slowly as possible.
The rationale of the strength of specula cast in this metal mould system, as compared with the treacherous brittleness of those cast in sand moulds, arises simply from the consolidation of the molten metal pool taking place first at the lower surface, next the metal base of the mould—the yet fluid alloy above satisfying the contractile requirements of that immediately beneath it; and so on in succession, until the last to consolidate is the top or upper stratum. Thus all risk of contractile tension, which is so dangerously eminent and inherent in the case of sand-mould castings, made of so exceedingly brittle an alloy as that of speculum metal, is entirely avoided. By the employment of these simple and effective improvements in the art of casting the specula for reflecting telescopes, and also by the contrivance and employment of mechanical means for grinding and polishing them, I at length completed my first 8-inch diameter speculum, and mounted it according to the Newtonian plan. I was most amply rewarded for all the anxious labour I had gone through in preparing it, by the glorious views it yielded me of the wonderful objects in the heavens at night. My enjoyment was in no small degree enhanced by the pleasure it gave to my father, and to many intimate friends. Amongst these was Sir David Brewster, who took a most lively and special interest in all my labours on this subject.
In later years I resumed my telescope making enjoyments, as a delightful and congenial relaxation from the ordinary run of my business occupations. I constructed several reflecting telescopes, of sizes from 10-inch to 20-inch diameter specula. I had also the pleasure of assisting other astronomical friends, by casting and grinding specula for them. Among these I may mention my late dear friend William Lassell, and my excellent friend Warren de la Rue, both of whom have indelibly recorded their names in the annals of astronomical science. I know of no subject connected with the pursuit of science which so abounds with exciting and delightful interest as that of constructing reflecting telescopes. It brings into play every principle of constructive art, with the inexpressibly glorious reward of a more intimate acquaintance with the sublime wonders of the heavens, I communicated in full detail all my improvements in the art of casting, grinding, and polishing the specula of reflecting telescopes, to the Literary and Philosophical Society of Manchester, illustrating my paper with many drawings. But as my paper was of considerable length, and as the illustrations would prove costly to engrave, it was not published in the Society's Transactions. They are still, however, kept in the library for reference by those who take a special interest in the subject.
1829. A Mode of transmitting Rotary Motion by means of a Flexible Shaft, formed of a Coiled Spiral Wire or Rod of Steel.
While assisting Mr. Maudslay in the execution of a special piece of machinery, in which it became necessary to have some holes drilled in rather inaccessible portions of the work in hand, and where the employment of the ordinary drill was impossible, it occurred to me that a flexible shaft, formed of a closely coiled spiral of steel wire, might enable us to transmit the requisite rotary motion to a drill attached to the end of this spiral shaft. Mr. Maudslay was much pleased with the notion, and I speedily put it in action by a close coiled spiral wire of about two feet in length.
This was found to transmit the requisite rotary motion to the drill at the end of the spiral with perfect and faithful efficiency. The difficulty was got over, to Mr. Maudslay's great satisfaction.
So far as I am aware, such a mode of transmitting rotary motion was new and original. The device was useful, and proved of essential service in other important applications. By a suitably close coiled spiral steel wire I have conveyed rotary motion quite round an obstacle, such as is indicated in the annexed figure.
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It has acted with perfect faithfulness from the winch handle at A to the drill at B. Any ingenious mechanic will be able to appreciate the value of such a flexible shaft in many applications. Four years ago I saw the same arrangement in action at a dentist's operating-room, when a drill was worked in the mouth of a patient to enable a decayed tooth to be stopped. It was said to be the last thing out in "Yankee notions." It was merely a replica of my flexible drill of 1829.
1829. A Mode of cutting Square or Hexgonal Collares Nuts or Bolt-Heads by means of a Revolving File or Cutter.