470 Progress of Invention, 



that of the atmosphere, ^ which he found imparted to the lime the 

 required decomposing power. , 



Vision under Water. — It is easy to distinguish objects at 

 moderate distances under water, provided the eye does not come 

 in contact with the fluid ; if it does, nothing more than a uniform 

 mass of light is perceptible. This is very easily explained : the 

 anterior surface of the eye forms a plano-convex lens with the water 

 in front of it, which possesses such a dispersive effect as prevents 

 the eye from any longer having the power of bringing the pencils 

 of light to a focus, and forming a picture on the retina. The 

 remedy, though apparently obvious enough, did not suggest itself 

 until recently ; it consists in counteracting the effect of the aqueous 

 lens by means of a convex glass lens. It is clear that various 

 forms of lens might be used for the purpose ; the fact being borne 

 in mind that, on account of the convexity of the eyeball, the concave 

 surface of the aqueous lens has a radius of curvature scarcely 

 greater than 0'31 of an inch. It is found, however, by calculation, 

 that a double convex lens of flint glass, the surfaces of which have a 

 radius of 0"48, answers the purpose ; not making allowance for the 

 peculiar kind of glass, or the adjustment required to suit the vision 

 of different persons. A suitable lens renders objects under water 

 distinctly visible : and it is therefore of great importance to pearl 

 divers, collectors of sponges, and others who are obliged to operate 

 under water, with the fluid in contact with their eyes ; but it is to 

 be observed that when it is used, the eye no longer possesses the 

 power Of adjusting itself to different distances : and hence objects 

 cannot be seen with it at a greater distance than about three yards. 



Economic Extraction op Vegetable Oils. — The oils found in 

 various seeds, etc., have been hitherto obtained usually by 

 means of pressure ; but this is both a troublesome and a 

 wasteful method. It has been found that any of the hydro- 

 carbons obtained from petroleum or other mineral oils, or from 

 asphalte, coal, slate, etc., and which boil at a temperature lower 

 than 100° C, afford a means of extraction which is far better in 

 every respect. The seeds, after having been bruised, are placed in 

 a vessel which is capable of being closed hermetically, and the 

 hydro-carbons are then introduced into the vessel. The oils are 

 dissolved ; and the solution having been run off, the hydro-carbons 

 are removed by distillation, which is effected by means of steam that 

 is made to pass through them, by means of a helical tube in the interior 

 of the vessel in which the distillation is effected. Before the seeds 

 and the hydro- carbons are brought into contact, they are slightly 

 warmed ; and the same seeds are to be acted [on successively, with 

 two or more different portions of the solvent, that the whole of the 

 oil may be extracted. 



Permanently Plastic Modelling Clay. — The rapidity with which 

 ordinary modelling clay dries, is a source of great inconvenience to 

 sculptors, etc. ; but the difficulty arising from this circumstance may 

 be obviated by very [simple means. The fact that glycerine has no 

 tendency to dry in atmospheric air has been already used with advan- 

 tage. Its latest application consists in its employment as a means of 



