CHAPTER IV 



THE RADIANT AND ILLUMINATION 



One of the most important primary ques- 

 tions confronting the beginner in photo-micro- 

 graphy is what form of radiant or illuminant, 

 within his means, will be the best for practical 

 use. If he be in a position to choose whatever 

 he likes, then a considerable range of light 

 sources is open to him. First and by far the 

 best is that of direct sunlight, regulated and 

 controlled by means of a heliostat. This is 

 the purest and most actinic of all radiants, 

 making possible the very shortest exposures 

 and yielding negatives all other conditions 

 being favorable of unsurpassed brilliance 

 and perfection. In this country, blessed with 

 so many days of sunshine, it is for the day 

 worker a very certain and reliable radiant ; in 

 others England, for example sunny days 

 are so rare as to practically debar it from use. 

 It is not within the scope of the present work 

 to do more than refer to its preeminent merit, 

 and to advise those who possibly can employ 

 its perfect rays to do so. Diffused daylight is 



