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POPULAR SCIENCE REVIEW. 
on the whole he prefers the first form of u double illumination ” as equally 
satisfactory and far less troublesome. 
Mr. Collins' Light Corrector. — An ingenious bit of apparatus has been 
devised by Mr. Charles Collins (17, Great Portland Street). It consists of 
a brass stage-plate with a groove in which rotates a diaphragm of four 
apertures, one of them being open and the other containing blue glasses of 
special tint, and one with a finely-ground surface. These effectually cor- 
rect the yellowness of all artificial illumination, making the light soft and 
agreeable to the eyesight as well as improving the definition. It is in fact 
an improvement on Rainey’s Light Modifier so as to obtain more varied 
effects, and does not require any special fitting, as it can be used on any 
microscope. 
A Curious Fact in JBichromatic Vision has been observed and described by 
Mr. J. W. Stephenson, F.R.M.S. He says, as of course is known to most 
students of optics, that, by the aid of a double-image prism and a film of 
selenite, two images may be shown in the field of the microscope, the 
colours of which will be complementary the one to the other, and that 
when these images overlap, the resulting image will be, as far as the over- 
lapping extends, of white light ; but it is not, he thinks, so well known 
that when, by a suitable arrangement, different colours are made to occupy 
the two fields of a binocular, the resultant is a combination of such colours, 
and that if these are complementary to one another, the sensation of colour 
induced in the brain by the retina of one eye, is neutralised by that which 
reaches it through the instrumentality of the other, and that by the com- 
bination of the two the sensation of colour is entirely lost. This, however, 
Mr. Stephenson observed in the most convincing way. The fact is a little 
curious, and we think, as yet, is insufficiently explained. — Monthly Micro- 
scopical Journal , May 1872. 
The Two Best Test Objects. — Dr. Col. Woodward says that Amphipleura 
pellucida is a useful and valuable test for immersion objectives of |th inch 
focal length or less. Lower powers can only hope to resolve it if possessed 
of excessive angular aperture. When, however, it is desired to discriminate 
between small differences in the excellence of objectives intended for the 
most exquisite resolution, a more subtle test is required, and this will be 
found in the nineteen- band plate of Nobert, by those who take proper pre- 
cautions in its use. Those, however, who believe they have secured reso- 
lution whenever they see lines in the higher bands of the plate, without 
duly considering their number, must not be surprised if objectives they 
have accepted as resolving the ultimate bands of the plate fail to show the 
striae on even the coarsest frustules of the Amphipleura pellucida. — Monthly 
Microscopical Journal , April. 
PHYSICS. 
Death of Professor Morse. — We regret being obliged to announce the 
death of Professor Samuel Finley Breeze Morse, which took place at his 
residence in New York city, on April 4, at the advanced age of eighty-one 
