514 HENRY LAURENS AND HENRY D. HOOKER, JR. 



The radiant energy of the next three lights was then equated by mov- 

 ing the spectrometer away from the lamp, without disturbing the 

 position of the reflector. 



Table 2 gives a complete summary of all the conditions necessary for 

 duplicating our apparatus and verifying our m.easm-em.ents. The 

 range of wave-lengths for each light, the point at which the wave- 

 length drum must be set, the width of the diaphragm, slit in the tele- 

 scope, the distance measured on the drum, between the end-points of 

 the range of wave-lengths, the range of the wave-leng-ths in question 

 on either side of the D Hne used in determming the width of the slit, 

 and the distance between the lamp and the slit of the collimator. 



CONCLUSION 



It seems of sufficient interest to restate briefly the advantages of the 

 apparatus which we have described. 



That it is perfect in the direction for which we have been arguing 

 is not contended, but it certainly represents a distinct advance over 

 anything that has been described for the comparative study of the 

 relative physiological value of colored light in an equal energy spec- 

 trum. The degree of error involved is, in our opinion, of much smaller 

 magnitude than the relative degree of sensitivity in the physiological 

 work contemplated. 



By means of the apparatus, in the first place, a series of brilliant 

 colored fights of high purity and saturation are obtained, each of which 

 is a band including a fairly small num.ber of wave-lengths, the same 

 for all, and equal in radiant energy content. Therefore no corrections 

 are necessary for this factor. Furthermore, the entii-e apparatus is 

 easily adjusted and any light obtained with ease. By it an exact speci- 

 fication of the intensity of the various spectral fights is given, the ex- 

 perimental conditions are rendered reproducible and an exact repeti- 

 tion of the experiments made possible. 



We are at present engaged in a series of investigations deafing with 

 the relative stim.ulating values of these lights on lower organisms and 

 on the eyes of higher form.s, as well as the study of chlorophyfi assimi- 

 lation and decomposition. But there are various causes which make the 

 completion of any but a small part of this work in the immediate future 

 doubtful. Owing to the conditions occasioned by the great war it is 

 impossible to obtain a spectrometer from. England. The spectrome- 

 ter which we are at present using is borrowed from the chemical 



