PATENTS. 



655 



band may wind in either direction on the bar- 

 rel. Connecting rods, E, F, extend to each 

 end of the car, where they are attached to 

 levers shown in 1. In stopping the car, the 

 driver moves the lever, carrying the lower 

 wheel B against the friction-druru. This re- 

 volves the barrel D, and through the band 

 revolves the case G, coiling the spring, the 

 friction-wheel B also operating on the axle as 

 a brake to stop the car. When the car is to 

 be started, the driver presses with his foot 

 upon a foot-plate, which, acting through the 

 chain K, releases the ratchet. At the same 

 time he pulls back the lever and brings the 

 upper wheel in contact with the friction- 

 drum A, so that, as the spring expends its force 

 in starting the car, the band is rewound and is 

 again ready for service on the outside of the 

 spring-case G. A different manipulation, un- 

 necessary to describe here, applies the force of 

 the spring to backing the car, if desired. 



Construction of Propeller Strews. The draught- 

 ing and making of models of propeller screws 

 has hitherto been one of the most difficult of the 

 mechanical problems, but M. G. Trouve has so 

 simplified the process that any mechanic can 

 make a model of any desired pitch. A cylin- 

 der (B, Fig. 9), the size of the boss of the in- 

 tended screw, is placed in an ordinary gear 

 lathe, and helicoidal grooves are cut in it of 



the desired pitch, and of a width and depth 

 corresponding with a series of metallic rods. 

 Eetaining plates are fastened to the ends of the 

 cylinder by means of thumb-screws, and the 

 rods are then placed in the grooves and crowd- 

 ed closely together (0, Fig. 9). They arrange 

 themselves, of necessity, divergently in a per- 

 fect helicoid of easily determined pitch, and 

 only need to be connected at the top, and have 

 the interspaces filled with some suitable ma- 

 terial to form a complete model of a screw 



from which castings can be made. The blades, 

 once formed, can be cut to any desired shape. 

 Washing Photograph Plates. A simple device 

 whereby a large number of developed plates 

 can be submitted to a gentle flow of water or 

 other fluid is shown herewith. The main sup- 



ply of fluid is placed in a vessel, A, and set on 

 an elevated support. Below, any number of 

 pans are arranged, slightly tilted, one overlap- 

 ping another, and a pitcher standing so that its 

 lip overhangs the uppermost pan. Two glass 

 tubes and a short length of India-rubber tub- 

 ing furnish a siphon, which only needs to be 

 put in operation to set the current in motion, 

 when it will run until the pail is empty. If 

 the overflow from the lowermost pan is re- 

 ceived in another suitable vessel, the fluid can 

 be retransferred to A, and made to do duty 

 repeatedly. If no pitcher is procurable having 

 a sufficiently depressed lip, a bit of bent wire, 

 or a bent glass rod, laid in the channel of the 

 lip, and hanging downward toward the upper 

 pan, will serve to guide the overflow. By this 

 means some of the most tedious operations of 

 photography may be greatly expedited. A 

 number of small blocks of wood may serve as 

 adjustable supports for the pans. 



A Simple Fire-Escape. In view of several ter- 

 rible warnings, the best hotels are providing 

 fire-escapes for their guests, and it is to be 

 hoped that laws will be passed making it 

 obligatory upon all hotel proprietors to fol- 

 low their example. A rope is the most sim- 

 ple means of escape from the window of a 

 burning building, but only an athlete can de- 

 scend a rope safely without aid. The device 

 shown herewith seems to make it possible for 

 any one to perform this otherwise difficult feat 

 with ease. Fig. 12 shows with sufficient dis- 

 tinctness the arrangement of the rope, clutch, 

 and belt. Fig. 11 "shows the practical opera- 

 tion. The upper end of the rope is made 

 fast near the window, and the lower end is 

 thrown out. The rope, it will be seen, takes a 

 turn around a pin in the clutch, and then passes 

 between two handles. Grasping these handles 

 with one hand, the operator sits on the window- 



