58 G. C. Hutchins — New Photographic Spectroscope. 



ing proportion of inert materials would collect in the lower 

 layers of the moving ice. 



3. The accumulation of such materials would tend to retard 

 the motion of the lower portions of the glacier; and finally, 

 when they formed a sufficiently great proportion of the mass, 

 all motion of the lower portion would cease and a permanent 

 deposit would begin and continue to be made. 



4. Other masses of detritus might be deposited at the foot 

 of the glacial ice-sheet as a terminal moraine, and still other 

 masses on the top of the already formed deposit when the 

 glacier finally melted. 



Art. VIII. — A New Photographic Spectroscope; by C. C. 



Hutchins. 



The constant demands of spectrum analysis for ever increas- 

 ing accuracy can be satisfied only by instruments of the highest 

 dispersion and most-perfect defining powers, and when applied 

 to photography the dispersion must be produced directly, and 

 not by enlarging lenses at the camera. The large apparatus of 

 Rowland does this most beautifully, as the writer, who has used 

 it for the past year, can testify ; but the fact that a large room 

 must be set aside for its accommodation, and moreover that the 

 large concave gratings are very difficult to obtain, will forbid 

 its use to most workers. 



I have therefore devised the following simple, and it would 

 seem upon short trial, effective arrangement for producing the 

 desired results : 



A rather long slit is placed at the focus of a crown glass (or 

 better, quartz) lens of forty feet focus. The ray from the slit, 

 after passing through the lens falls upon a large flat grating 

 mounted to turn about an axis passing through the middle line 

 of the ruled surface. The spectrum is projected by the same 

 lens upon a horizontal arc of forty feet radius, and is observed 

 a little to one side or above the slit. The spectrum will not 

 be normal throughout its length unless the radius of projection 

 be kept constant. I think- this had better be provided for by 

 employing two lenses of crown glass, the one nearer the grating 

 fixed, the other movable, than by the use of a corrected lens, 

 to avoid the absorption of flint glass in the achromatic com- 

 bination. 



More or less absorption when glass is used is unavoidable, 

 and this, with the variation of the focal plane of the lens for 

 light of different wave lengths, constitutes the most serious de- 

 fects of the apparatus, — defects which are avoided in the 



