178 



THE AMERICAI^ MONTHLY 



[September, 



rican makers have been overlooked — 

 yet the author should know that some 

 of the best designed stands now in 

 the market are manufactured here. 



With regard to objectives, Dr. Car- 

 penter still ably defends the position 

 which he has always held, that mod- 

 erate angular apertures are the best 

 for general use. 



In the chapter on the preparation 

 and mounting of objects, many 

 changes and additions have been 

 made, whereby it is greatly improved. 

 Considerable new matter has been 

 added to the part which treats of 

 the lower forms of plant-life. The 

 development-history of Bacillus an- 

 thracis is quite fully recounted, with 

 the aid of illustrations, and the Myx- 

 omycetes are treated at considerable 

 length. 



The chapter on the Protozoa has 

 been greatly extended and a number 

 of illustrations have been added ; 

 the Rhizopoda are more fully de- 

 scribed than in the previous edition, 

 but the diagrammatic representation 

 of Amxba proteus, on page 486, shows 

 a " villous tuft " which is not charac- 

 teristic of that species as defined by 

 Leidy. 



A good summary of the researches 

 of Messrs. Dallinger and Drysdale 

 upon flagellate infusoria is given, 

 and in the same chapter much new 

 matter has been added, with new cuts, 

 relative to the microscopic forms of 

 animal-life. The department of mi- 

 croscopical lithology and mineralogy 

 is very satisfactory indeed, and it is 

 particularly valuable on account of 

 the references to other sources of in- 

 formation, which are very well 

 chosen. On the whole, the book is 

 greatly improved in many ways, and 

 we do not hesitate to declare our belief 

 that it is the best book in the English 

 language for general microscopists. 



CORRESPONDENCE. 



To THE Editor : — How close lines 

 have been resolved, and how close they 

 can be resolved, are questions of interest 



not only to the microscopist, but also to 

 the physicist, the physiologist and the 

 instrument maker. 



Nobert's old theory, that it was impos- 

 sible to see lines closer than 85,000 (?) to 

 the inch has been disproved for fourteen 

 years. There have been published in 

 journals, within the last two years, claims 

 that lines 120,000 to the inch have been re- 

 solved. Many who have experimented in 

 this work doubt if it has ever been done. 



The deciding between the true lines, 

 and spectral or diffraction lines (Abbe's 

 theory requires that the diffraction lines 

 only should be visible) can be done only 

 by one who has great experience in this 

 work ; and one who claims to have seen 

 such close lines should be prepared with 

 satisfactory evidence of his experience, 

 and of the fact. 



It is known that there are in this coun- 

 try two plates ruled by Nobert twice as 

 close — so he said — as his noted nineteenth- 

 band plate. The last information about 

 them was, that with the largest battery 

 of the best objectives in existence, with 

 the most extensive equipment of appara- 

 tus for all illuminations, a most expe- 

 rienced observer " could not get one peg 

 beyond the 120,000 to the inch." 



It is to be hoped that your correspon- 

 dents will accept your invitation and com- 

 municate what they know, and the evi- 

 dence of what has been done in this line. 



While one may hope that lenses may 

 yet be made to resolve 120,000 lines to 

 the inch, we must yet say that satisfactory 

 evidence that it has been done is still 

 lacking. 



Carl Reddots. 



To THE Editor : — With thanks to 

 yourself and Mr. Hanaman for the valu- 

 able practical " Notes on Microscopical 

 Technology " recently given to your read- 

 ers, I wish to suggest an improvement 

 upon his last suggestion. He says truly 

 that, " From the fact that the glass slides 

 are not perfect rectangles, it is necessary 

 to place the same corners in the same 

 clutches of the self-centering turn-table." 

 And he adds that, " the simplest way to 

 do this is to mark one of the clutches with 

 a cross, and similarly to mark with a file 

 or writing diamond one corner of each 

 slide while cleaning it." I think it will be 

 found quite as simple, and for obvious 

 reasons much better, to pursue the follow- 

 ing plan which I devised a couple of years 

 ago and have constantly applied ever 

 since. Mark one of the clutches as indi- 



