Nature . be connected in series with one or two of the lampsordinarily used on the circuit. Most electric lamps havelooped filaments, and are not so well adapted for theobservation. When the dimmed lamp is looked at from a distanceof a few feet through a lens of about 6 inches focallength, held close to the eye, the patch of luminosityformed upon the retina appears to be made up of acrowd of separate images of the filament, some being. brighter than others, as represented in Kig. i, Whenthe observer is near the lamp, the number of images iscomparatively small ; as he retires, it gradually incr
Nature . be connected in series with one or two of the lampsordinarily used on the circuit. Most electric lamps havelooped filaments, and are not so well adapted for theobservation. When the dimmed lamp is looked at from a distanceof a few feet through a lens of about 6 inches focallength, held close to the eye, the patch of luminosityformed upon the retina appears to be made up of acrowd of separate images of the filament, some being. brighter than others, as represented in Kig. i, Whenthe observer is near the lamp, the number of images iscomparatively small ; as he retires, it gradually increases,but after a certain distance has been reached thedefinition of the images becomes impaired, and theycan no longer be easily distinguished. The method ofobservation as thus described may obviously be varied, The photogrnphs, Figs, i to 4.(luction. In the each pictuof separate images of the tilament. NO. 1537, VOL. 59] too delicate for satisfactory rcpro-s easily seen to be entirely composcii and, indeed, an experienced observer can put his eysufficiently out of focus without the aid of any lens. To assist in analysing the luminous field, an adjustabl—slit, taken from a spectroscope, was interposed betweenthe eye and the lens. The appearance presented by thefilament when the slit was made i(j inch (o3 mm.) wide,is very well imitated in Figs. 2, 3 and 4, which show thf^effect with the slit in hoiizontal, vertica
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