758 



SCIENTIFIC RECREATIONS. 



apartment is then perfectly retained by means of the air between the double 

 windows. 



In the same way the double window is not less useful during the 

 summer, for it prevents the entrance of the heated air into the house. The 

 double window may therefore be compared to the bournous of the Arab and 

 the cloak of the Spaniard, which preserves from heat as well as guards 

 against cold. 



The double windows also perform another service. The glasses form 

 a hot-house. The sun heats the air which is enclosed, and thus between 

 the panes ferns and even vines will flourish. The windows are very easy to 

 make, and in the event of any reader desiring to construct one or more, we 

 give the dimensions. (See fig. 885.) 



I T T, is the exterior frame of the window. The two panes are mounted 

 On a frame of wood, and are represented by A A' and B B'. The sashes are 

 represented apart, P and P' are the shutters of sheet iron, which, if the walls 

 be not so thick as represented, can be replaced by a spring-blind, which 

 descends between the windows. 



SEWING MACHINE WORKED BY A DOG. 



Animals have been employed for all time to draw carriages and the 

 plough, etc. But these animal " motors " are usually employed under de- 

 fective conditions, and there- 

 fore without full profit. The 

 inert mass of the animals 

 remains quite unutilized, his 

 force only is employed, and 

 there are many objections on 

 the score of humanity, as well 

 as from a mechanical stand- 

 point, and great muscular 

 tension with suffering may be 

 inflicted upon an animal which 

 is continually mounting a wheel 

 or such contrivance for raising 

 water. There was in the Paris 

 Exhibition a threshing machine 

 put in motion by a horse walk- 

 ing upon a pair of rollers which 

 constituted an " endless " way, 

 and we will now briefly de- 



Fig. 886. Sewing machine worked by a dog. 



scribe a machine which utilizes 



animal force and weight It is the invention of M. Richard of Paris, 

 who has made many mechanical apparatus for industrial purposes. 



