ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



399 



larger publication, " Photomicrography," and includes several novelties. 

 In the table of exposure factors for Wratten " M " filters with Wratten 

 " M " plates (p. 11) factors are given for use with the recently intro- 

 duced pointolite lamp instead of the previous cohimn of Nernst factors. 

 In addition to the nine filters forming the well-known " M " set, thi'ee 

 others (K8, 78, 96) are described which may be of use to microscopists. 

 K3 is a luminosity screen for orthochromatic reproduction, and should be 

 used if daylight or equivalent daylight is to be employed. No. 78 is a 

 filter primarily intended for the conversion of the light from a metal- 

 filament lamp into the visual equivalent of average daylight. It may 

 also be used with the pointolite lamp and with the smaller-powered 

 half-watt lamps, and, less efficiently, with incandescent gas or oil. It 

 gives a very close approximation to daylight, and will be found very 

 useful and restful to the eyes in the case of long-continued visual 

 observation. Xo. 96 (D 1-5) is a neutral tint filter, and transmits 

 about 3 p.c. of the incident light for use when focussing with a strong 

 illuminant, or for lengthening the exposure (about thirty-three times) 

 when inconveniently short, as with low powers. It does not alter the 

 contrast obtained with coloured filters. The Kodak Company hope 

 soon to be able to supply a blue filter, of dominant wave-length 47U0, 





Fig. 1. 



Fig. 2. 



Illusteations showing the Control of Detail by the use of 



Wratten " M " Filtees. 



Fuchsin-stained Section. T.S. Stem of Clematis flammula X 40. 

 Fig. 1. Ordinary plate, no filter. Fig. 2. Wratten " M " plate, B and G filters. 



