188 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



the substance under examination, in order that we may be 

 able to distinguish minute spherules, cylinders, or other 

 bodies from each other. In the course of his paper, Mr. 

 Pigott states that no glass yet constructed, whether micro- 

 scopic or telescopic, lias been adequate to present to the 

 eye the real size of the image of the sun reflected from a 

 small spherule. With a telescope, the disk, which ought to 

 be the -j^Vo f an ich, appears something like the -^ of an 

 inch in diameter, or the spurious disk is five hundred times 

 larger than the reality. He concludes from many careful 

 experiments that microscope object-glasses are more finely 

 constructed than the telescopic, but that great improve- 

 ments are still necessary in that direction. Monthly Micro- 

 scopic Journal, Feb., 1875, 55. 



EECENT IMPROVEMENTS IN THE MICROSCOPE. 



The President of the Royal Microscopic Society, in his 

 late anniversary address, states that the past year has been 

 marked with decided improvements in the construction of 

 microscope object-glasses. A remarkably fine one -eighth 

 inch has been made by Messrs. Powell & Lealand. The 

 image borne by this lens bears amplification by deep eye- 

 pieces exceedingly well. Mr. Wenham has constructed a 

 one-seventh inch on an improved formula, obtained by sub- 

 stituting two plano-convex lenses for the single plano-con- 

 vex posterior lens originally employed. The new lenses 

 are superior in definition, and far superior in clearness and 

 absence of fog or milkiness, to any other objective known to 

 him. As regards fog, this defect is very conspicuous in the 

 one-sixth inch made by Ross, which is constructed of a sin- 

 gle front lens followed by three cemented combinations. 

 There are some reasons for surmising that fog is partly due 

 to the multiplication of cemented contact surfaces ; and if 

 this be so, the general principles of analysis would lead to 

 the conclusion that the amount of the defect in question 

 would be in proportion to the square of the number of ce- 

 mented surfaces. Thus, this one-sixth inch of Ross, which 

 has four cemented surfaces, might be expected to present 

 four times as much foo: from that cause as the one-seventh 

 inch recently made by Mr. Wenham, which has only two 

 cemented surfaces. Monthly Microscopic Journal, 1875, 98. 



