?78 French Kational Insiiluie. 



between the diflerent gases and light. M. Biot himself will 

 read an extract of it to the Institute. 



There will also be read a memoir bv count Rumford, on 

 the adhesion of the molecules of water; but we shall give 

 the principal results of the observations made by this learned 

 philanthropist, upon the dupersion of the light of Imnps brj 

 the mcar.s nf shades end globes of ground glass. 



The facility with which the eve distiii.2ui-hes objects, 

 does not njerely depend upon the intensity of the light 

 which illuminates tliem, it also depends much upon the 

 shadows ; if they are simple and well marked, the vision is 

 distinct : but if the light comes from several sides at once, 

 there are several shades which confound and weaken them ; 

 hence we see badly even with a good deal of light. A good 

 distribution of the light is therefore important forceconomv, 

 and particularly for the preservation of the eyes. 



The direct rays of a lamp, with a double current of air, 

 fatigue the sight. In order to lessen this inconvenience, 

 shades of different kinds have been invented, and at last 

 globes of ground glass. What renders the use of the latfer 

 less common is the fear of losing too much light. Nobody, 

 in France ac least, has attacked this prejudice, but count 

 Rumford demonstrates, by an experiment verv easy to repeat, 

 that the loss of light is almost insensible. The surface of 

 ground glass, full of furrows and roughnesses, presents to 

 the light a number of minute smooth planes, but differently 

 inclined, which dispersing the light, render it softer, and 

 distribute it in such a manner as to carry a more uniform 

 clearness to every corner of the piece which we wish to 

 illuminate. 



Tliis advantage is not the only one possessed by ground 

 glass. Being substituted instead of polished glass, in the 

 clazing of windows, it will spread the light of day with 

 more equality in the highest as well as in the lowest situa- 

 tions, in the furthest as well as the nearest; and this remark 

 is particularly useful for great cities, where the confined 

 width of the streets and the height of the houses, only 

 admit of the light penetrating very obliquely. The author 



has 



