40 SCIENTIFIC AMUSEMENTS. ' 



under the pressure. A strong tin can filled one-third with water 

 and made to boil over a lamp may be used to illustrate the fact of 

 increased pressure being produced by confining the steam ; a cork 

 placed in the mouth (not jammed in too hard) whilst gently boil- 

 ing will in a few seconds be driven out with a "pop" by the 

 pressure. If the cork be too firmly fixed, the pressure may very 

 likely burst the can instead of projecting the cork, scattering 

 scalding water around. 



Expt. 33. To make a Model Eotating Machine working by 

 Steam Pressure. When water is boiled in a vessel provided with 

 a narrow pipe through which the steam can issue, a continuous 

 current of vapour will pass off through the jet as long as the water 

 boils. If a small model windmill be placed in the current of 

 steam it will be turned round just as it would by wind. Several 

 toys based on this principle are sold the "Dancing Nigger" 

 is one of the kind; the jet of steam from a small metal boiler 

 heated by a spirit-lamp impinges on the floatboards of an arrange- 

 ment like a waterwheel and so makes this 

 revolve, thereby setting in motion a sort of 

 table under the feet of a jointed figure of a negro 

 supported by a wire, and so shaking the figure 

 and causing it to jump and dance about in a 

 comical way. 



Expt. 34. Steam Reaction Machine. Fig. 20 

 represents another simple form of rotating 

 machine, where the motive power is the pressure 

 of steam generated inside a glass bulb by heating 

 with a lamp and escaping therefrom by means of 

 two curved jets. It requires a good deal of 

 expertness in glass-blowing to blow the bulb and 

 jets successfully; but the arrangement may be 

 purchased cheaply at the instrument makers. 

 To fill the bulb, it is held by means of the wire 

 support so that one of the jets is undermost and 

 dips into water which is thus sucked into the 

 bulb by means of the other jet, conveniently by 

 slipping a bit of fine india-rubber tube over the 

 nozzle and sucking through it. By employing 

 lavender water, or ordinary water scented with 

 Fig. 20. Steam a ^ ew drops of eau-de-Cologne, &c., the arrange- 

 Reaction Machine, ment may be used as a perfume vaporiser to scent 



an apartment. 



This experiment is especially interesting from the fact that the 

 very earliest machine ever made whereby motion was produced by 



