MECHANICAL AND USEFUL ARTS. 123 



ment is placed, the result is marvellous : there is produced from the 

 most unlikely objects, such as scraps of paper-hangings, blots of 

 ink, leaves, flowers, bits of lace, &c, an endless series of new and 

 really beautiful designs. The debusscope, although of the same 

 species, possesses an advantage over the kaleidoscope. The latter is 

 merely suggestive of any effect likely to prove useful to a designer ; 

 there are no means of retaining any particular pattern which may 

 literally " turn up" until it can be transferred to paper. The debus- 

 scope gives the design, and that in such a manner that it can be 

 made stationary at pleasure until copied; it therefore recommends 

 itself at once as an inexhaustible source of new patterns to draughts- 

 men, calico printers, dyers, paperhangers, painters, and others ; and. 

 as it is produced and sold at a price which brings it easily within 

 the reach of all such trades, we have no doubt that it will soon be 

 extensively used. 



MACHINERY FOR TEACHING. 



Mr. Smallet, of King's College, has constructed two very effi- 

 cient aids to teachers of elementary science, which are manufactured 

 by Messrs. Elliott, in the Strand. The first is a machine demonstra- 

 tive of the composition of forces, in which the pressure equivalent 

 to two other pressures is shown to be represented by the diagonal, 

 when the component pressures are represented by the sides. The 

 second is a very simple revolving radius, which carries with it 

 a pendulous perpendicular, both graduated, as also is the line 

 of the base. The character and the approximate values of the 

 trigonomical functions are exhibited, in all parts of the revo- 

 lution, in a manner singularly clear and free from the confusion 

 which attends a diagram of several instances. There are also some 

 illustrations of the disused linear definitions. 



THE TROCHEIDOSCOPE. 



This beautiful instrument has been constructed by Messrs. Home 

 and Thornthwaite, of Newgate-street, and is the invention of 

 Mr. Thomas Goodchild, architect, of Guildford, designed for dis- 

 playing . various effects of the combination of colours upon a 

 novel principle — some of them in a most brilliant manner. The 

 Trocheidoscope is a train of wheelwork, so arranged that by 

 gently turning the handle the horizontal disc table is made 

 to revolve at varying speeds, at the will of the operator, 

 from fifty to two thousand revolutions per minute. In the 

 centre of the disc table is a carefully-fitted spindle, with a screw 

 and flange at the lower end, and a shoulder at the upper end, 

 just under which is a universal joint for adjusting the position 

 of the topmost portion, upon which the patterns or devices are to 

 be hung when exhibited. Proceeding from the side of the instru- 

 ment is an arm of brass, with a small appendage or hook at the 

 top for receiving the strings of the patterns, and a spring to act as 

 a check upon the discs used in the Protean experiments. The spindle 

 is jointed near the top to give a peculiar vibratory motion to the 

 pattern when fitted. As the spindle revolves it strikes the sides of 



