136 



THE AMERICAN MONTHLY 



[July, 



Whei"e strong resolving power was 

 needed, oblique pencils of sunlight 

 from the heliostat would outrival any 

 other illumination ; but much care 

 was necessary not to injure the sight, 

 and on the whole he could not recom- 

 mend its general use except for pho- 

 tographing. Diffused daylight was 

 too uncertain — too variable — for ac- 

 curate testing of objectives. It was 

 not possible to get w^ith diffused day- 

 light the absolutely best image that 

 an objective would produce. A really 

 critical image could only be seen with 

 artificial light, and with a good con- 

 denser and diaphragms. He did not 

 mean to say that no good work could 

 be done with diffused daylight, for 

 excellent work was done with low or 

 medium powers ; but he insisted that 

 it was not possible to do any such 

 critical work as testing objectives b}^ 

 daylight as thoroughly as it could be 

 done by artificial light. With day- 

 light and mirror only there was 

 milkiness, and what he might term 

 "glaze." The milkiness could be 

 got rid of by a diaphragm, and the 

 *•■' glaze " by using a ground glass be- 

 hind the object. Unless a condenser 

 were used there would always be 

 found a falling off' of the quality of 

 the image with all powers higher 

 than f. From long experience in 

 working with the microscope he felt 

 justified in asserting that on the whole 

 daylight was more trying to the sight 

 than lamp-light. Every one would 

 understand the importance of keeping 

 oft' stray light from the stage, &c. 

 An ordinary paraffin lamp having a 

 wick of half an inch would ansvi^er 

 most purposes admirably, and with 

 low powers gi'ound glass should be 

 employed either -with or without con- 

 denser. The image of the flame 

 could be projected in the ground 

 glass, nearer or further from the ob- 

 ject. The oxy-hydrogen light might 

 be serviceable for resolving such tests 

 as Nobert's lines. The incandescent 

 lamp he regarded as entirely a failure 

 for microscopical purposes. 

 (To be contimied.^ 



EDITORIAL. 



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The regular receipt of the Journal will be an ac- 

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American Society of Micro- 

 scopiSTS. — The meeting of the Amei"- 

 ican Society this year takes place at 

 Rochester, N. Y., beginning on the 

 19th of August, and continuing four 

 days. The British Association meets 

 at Montreal on the 37th of August, 

 and the American Association at 

 Philadelphia, beginning September 

 3d. Those who desire will, therefore, 

 be enabled to attend the three meet- 

 ings. 



The meeting at Rochester prom- 

 ises to be well attended, and great 

 preparations are in progress, in antici- 

 pation of a large gathering of micro- 

 scopists. On page 117 of the June 

 number will be found a note in regard 

 to a series of demonstrations of prac- 

 tical w'ork, which promise to be a 

 useful feature of the meeting. The 

 Rochester Acadeni}^ of Sciences has 

 made announcement of a soiree to be 

 given on the 21st inst. ' It is desired 

 that the exhibits be as numerous and 

 complete as possible, and all micro- 

 scopists are invited to assist on that 

 occasion. The committee in charge 

 desire to ascertain at the earliest prac- 

 ticable date how far they can rely 

 upon the co-operation of members 

 and others ; the number of micro- 

 scopes for which to provide tables, 

 illumination, etc., in order to intelli- 

 gently make the proper arrange- 

 ments.' A blank is sent out with 

 the announcement, to be filled up by 

 intending exhibitors. It has been 

 carefully prepared and ought to sei-ve 

 its purpose well. It bears evidence 

 that the preparations are in charge of 

 competent and energetic persons, and 



