22 Messrs. Morton, Mayer, and Thomas on 



made by them in the physical laboratory of the Stevens Insti- 

 tute of Technology, possess some general interest as being the 

 first full and accurate series of determinations, giving the fun- 

 damental properties of one of these instruments. 



The lamp in question was one of the paper-horseshoe style, 

 No. 154, given by Mr. Edison to the editors of the 'Scien- 

 tific American,' and by them kindly loaned to us. 



We have failed to obtain other lamps directly from Mr. 

 Edison, seemingly because of the offence taken at Menlo Park 

 to the emphatic contradiction which one of us thought it right 

 to give at the very outset to the unfounded claims for Mr. 

 Edison's lamp, which were then published by some of the daily 

 papers. 



The lamp here described is certainly a fair specimen of the 

 type to which it belongs, as appears from a general comparison 

 of results with those obtained by the scientific men who re- 

 cently measured a number of these lamps at Menlo Park under 

 the auspices of Mr. Edison himself. 



. The work herein described has been in progress for nearly 

 two months, being frequently interrupted by the pressure of 

 other engagements. 



Our experiments naturally divide themselves into three 

 groups : — 



I. Determination of resistance of lamp as compared with 

 luminous power and with total heat developed. 



II. Determination of average of light given out by lamp in 

 all azimuths. 



III. Determination of current-strength in circuit corre- 

 sponding to various intensities of luminous power in lamp and 

 deflections of galvanometer. 



With these data, the determination of relation of luminous 

 power to energy expended in the lamp itself in producing the 

 same was a matter of direct calculation. 



I. Determination of the resistance of the carhon-loop of lamp 

 as compared ivith its luminous power and total heat developed. 

 — A preliminary experiment having shown that between 50 

 and 60 cells of a Grove battery, with active zinc surface of 20 

 square inches and platinum surface of 18 square inches in each 

 cell, were required to develop the requisite electric current, such 

 a battery was set up and connected piecemeal with the rest of 

 the apparatus arranged as follows. 



The battery- current was divided into two branches, which 

 traversed in opposite directions the two equal coils of a diffe- 

 rential galvanometer having *33 ohm resistance in each coil. 

 One branch then traversed the lamp, which was placed in a 

 Bunsen photometer made by Sugg, of London. The other 



