54 



MECHANICS. 



wards B, C D rises in" the vertical direc 

 tion. 



The wind acting on the sails of a 

 ship in one direction gives the vessel a 

 rectilinear motion in another direction. 



(1 06.) To convert continued rectilinear 

 motion into reciprocating rectilinear 

 motion. 



Let A B be a chain furnished with 

 wipers m, n, o. Let B be a frame 

 loaded with weights and furnished with 

 a wheel C, and let the frame be so fixed 



Fig. 92. 



with a'wheel on which similar teeth are 

 raised, the continued rectilinear motion 

 of the rack will produce continued cir- 

 cular motion in the wheel, and vice versa. 



A strap, or belt, passing round a 

 wheel, and turning it by its friction with 

 the surface or groove in which it works, 

 will attain the same end where the re- 

 sistance is not very great. An endless 

 strap may be used, in which case two 

 wheels will be necessary. 



But in cases where much resistance 

 is to be overcome, the friction of the 

 strap with the surface of the wheel would 

 not be sufficient to transmit the force. 

 In this case, however, a chain and rag- 

 wheel may be used. The chain some- 

 times lays hold of pins or hooks in the 

 wheel, as represented in Jig. 93, and 



Fig. 93. 





that it is incapable of any but a verti- 

 cal motion. As the chain is moved 

 continually in the direction A B, the 

 wheel C running up the surfaces of the 

 wipers will be elevated, and when it 

 passes the point of each wiper it will 

 fall into the space between that and the 

 succeeding one, and thus the frame B 

 will acquire a rectilinear motion up- 

 wards and downwards. 



(107.) To convert a continued rectili- 

 near motion into a continued circular^ 

 or vice versa. 



There are various methods of effect- 

 ing this. The wheel and axle is an 

 obvious instance where the continued 

 rotation of the power produces the con- 

 tinued rectilinear ascent of the weight, 

 or if the weight be permitted to descend, 

 its continued rectilinear descent will 

 give a continued rotation to the wheel. 



This may also be effected by a toothed 

 wheel working in a rack. A rack is a 

 straight bar on which teeth are raised. 

 If such a bar be placed in connexion 



Fig. 94. 



sometimes carries 

 pins upon it, which 

 enter notches in 

 the circumference 

 of the wheel, as in 

 fig- 94. 



A common screw 

 offers an instance 

 of the conversion of 

 continued circular 

 motion into conti- 

 nued rectilinear. 

 The power applied to the head of the 

 screw moves with continued circular 

 motion, and the screw itself advances 

 with continued rectilinear motion. 



The paddle-wheels of a steam-boat 

 and an undershot water-wheel are ex- 

 amples of a continued rectilinear motion 

 produced by a continued circular, and 

 of a continued circular produced by a 

 continued rectilinear. 



An overshot or breast -wheel is an 

 instance of continued rectilinear molion 

 producing continued chcular; also the 

 wind, acting on the arms of a windmill, 

 is another example of the same effect. 



The screw of Archimedes is an in- 

 stance of a continued circular motion 

 producing a continued rectilinear one. 

 (See Hydraulics, chap, ii.) 



