January 1, 1909] 



SCIENCE 



37 



plates. We have measured other bands as 

 follows : 



Extending from about X 4290 to X 4250 with 

 center at X 4267. 



Extending from X 4030 to X 3995 with center at 

 about X4015. 



Center at about X3915, less refrangible edge at 

 about X 3920. 



Center at about X 3795. 



Those at A. 426Y and A 3920 fall in the posi- 

 tion of the only lines (as contrasted with 

 bands) in the carbon spectrum in this region, 

 but we do not regard this as an identification. 



The tail extends out in very different inten- 

 sities from some of the knots ; thus A, 4Y37 has 

 only a small extent of tail, but the knots at 

 A473Y and 3883 give the appearance of a 

 greater development than the others in the 

 direction away from the tail, i. e., toward the 

 front of the head. 



Otherwise the spectral images of the tail 

 exhibit the same general structure shown by 

 direct photographs of the comet on the same 

 nights. No marked changes in the chemical 

 constitution of the tail have been observed by 

 us between October 28 and December 1. It is 

 interesting to note, however, that this simple 

 apparatus would have been competent to show 

 any differences in constitution such as called 

 for by Bredichin's theory, had it been used on 

 September 16, when the direction of the tail 

 changed through a large angle from its direc- 

 tion before and after that date. 



A detailed account of our study of these 

 plates, with reproductions of some of them, 

 will appear later in the Astrophysical Journal. 



Edwin B. Frost, 

 J. A. Parkhurst 



Yerkes Observatory, 

 December 2, 1908 



A SIMPLIFIED APPARATUS FOR DRAWING WITH THE 

 AID OF THE PROJECTION MICROSCOPE 



In a number of laboratories there are in use 

 devices for drawing by the aid of a projection 

 lantern. These vary in complexity from a 

 simple easel at which is traced the direct pro- 

 jection of the image, to comfortable dark 

 rooms especially equipped for this work and 

 with an apparatus for reflecting the image to 



the table at which the artist sits. The first 

 type is inconvenient and fatiguing, the second, 

 on account of both the expense and the space 

 demanded, is not available in every laboratory. 

 It was Professor S. H. Gage's complete and 

 excellent equipment that suggested the here- 

 described simple device, to be used in the lec- 

 ture-room where the projection outfit stands, 

 without duplication of apparatus or require- 

 ment of extra space. 



It consists merely of a rod holding a mirror 

 at an angle of exactly 45°, clamped to the 

 stand which carries the projection lantern or 

 the microprojection outfit. With this in use 

 one may sit at a table in a darkened room and 

 trace the projection of microscopic prepara- 

 tions, lantern-slides or of photographic nega- 

 tives. A glance at the diagram will show the 

 extreme simplicity of the parts involved. 



A, shown also in end-section at A', is a 

 piece of wood two by two inches and about 

 three feet long, grooved by means of a rabbet 

 plane so as to clamp firmly to the lantern 

 table (see A'). The arm B bears the two 

 grooved strips C which carry at an angle of 

 45° the mirror D. This casts the image on 

 the drawing surface E, where it may be traced 

 with ease. 



The magnification depends directly upon the 

 distance of the drawing board from the mirror. 

 Thus if the enlargement is two times when 

 line E-D is ten inches, the image will be en- 

 larged four times if line E-D is twenty inches. 



