188 ANNUAL OF SCIENTIFIC DISCOVERY. 



arise from the superficial layers of particles being highly, though still 

 imperfectly, transparent, and permitting the inferior layers to be seen 

 through them. This effect we see produced when many watch-glasses are 

 laid in a heap, or when a plate of transparent mica or talc being heated red 

 hot is thus separated into multitudes of thin layers, each of which, of 

 inconceivable thinness, is found to be highly transparent, while the entire 

 plate assumes the lustre of a plate of silver. This explanation receives a 

 very striking confirmation from the stereoscopic phenomena which he now 

 drew attention to. He then presented to the Section and described a very 

 simple and portable modification of the stereoscope, consisting of two len- 

 ticular prisms mounted in a frame like a double eye-glass. Upon examin- 

 ing with this two diagrams dra\vn, one for the right, the other for the left 

 eye, with lines suited to give the idea when viewed together of a pyramid, 

 cube, cone, or other mathematical solid, but the lines on one drawn on a 

 white ground, the other on a dark or colored ground, on viewing them 

 together the solid appeared with the metallic lustre. The author termed 

 it " Glance." This, he conceived, demonstrated his original idea to be 

 correct. 



ON IRRADIATION. 



Prof. "W. B. Rogers, in a paper read before the American Scientific 

 Association, divides the phenomena of irradiation into two distinct kinds. 

 When the sun glances from the surface of a polished steel ball, or when 

 we observe any brilliant light near the eye, the centre of illumination is 

 surrounded by a circle of rays, which are not stationary, but seem to have 

 a pulsatory motion, and the pupil of the eye contracts to protect it. This 

 is radiation of one sort. The second sort we see on observing lights at a 

 distance, as the stars ; or lights which are only bright comparatively, being 

 set on a dark back- ground. The radiation of such lights is not circular, 

 nor uniform. Different eyes give different patterns. The first may depend 

 on the fact that the rays pass through the edge of the iris, which are drawn 

 together when the pupil contracts, as it always does, to shut out the intense 

 light ; and the second form upon the irregularities of the edge of the iris, 

 which in no two individuals or eyes has precisely the same outline. 



DIOPTRIC REFRACTORS. 



It is well known to those who are acquainted with the principles of 

 optical science, that when light passes from one medium to another in any 

 direction not perpendicular to the surface dividing them, that direction 

 undergoes a sudden change, called refraction ; the amount of this change 

 of direction, or divergence, is dependent on the angle of incidence, as it is 

 called. To take advantage of this principle in utilizing to the utmost 

 extent the light derivable from gas and other burners, of the description in 

 every-day use, the dioptric refractor has been invented by Messrs Boygett 



