58 THE MICROSCOPE AND ITS REVELATIONS. 



costly wide-angled Objectives, which certain Microscopists, especially in 

 the United States, are now extolling as alone trustworthy. * In confirma- 

 tion of the foregoing remarks, the following additional authorities may 

 be cited: Dr. Beale, whose Hiscological experience no one can call in 

 question, says ("How to Work with the Microscope," 5th ed., p. 10): 

 "For ordinary work it will be found inconvenient if the object-glass, 

 " when in focus, comes too close to the object. This is a defect in 

 "glasses having a high angle of aperture. Such glasses admit much 

 "light, and define many structures of an exceedingly delicate nature 

 " which look confused when examined with ordinary powers. For gen- 

 " eral microscopic work, however, glasses of medium angular aperture 

 "are to be recommended. Glasses having an angle of 150 and upwards 

 "are valuable for investigations upon many very delicate and thin struc- 

 tures, such as the Diatomacece; but such powers are not well adapted 

 "for ordinary work." So Dr. Heneage Gibbes, who has been trained 

 under Dr. Klein, one of the most distinguished Histologists of the pres- 

 ent day, recommends the Student (" Practical Histology and Pathology," 

 p. 6) to get some good Microscopist to test the object-glasses he thinks of 

 purchasing; " and he should see that they are tested on some Histological 

 "object, and not on Diatoms, as the wide angles necessary for resolving 

 "test Diatomaceoe are the reverse of useful to the young histologist." 

 And Dr. Leidy, of Philadelphia, everywhere well known as a most able 

 Biological worker of large and varied experience, who has lately produced 

 an admirable Monograph (illustrated by 48 beautiful quarto-plates) on 

 the " Fresh-water Rhizopods of North America," makes a point, in his 

 Introduction (p. 3), of informing Students " that Microscopic observa- 

 " tions, such as those which form the basis of the present work, do not 

 " require elaborate and high-priced instruments;" the Student's Micro- 

 scopes of Zentmayer, Beck, or Hartnack, with a power of l-4th or l-5th 

 inch, and the occasional use of a l-8th or l-10th inch, furnishing all that 

 is needed. " I give the above statement," he adds, " not with any dis- 

 "positionto detract from the value of the various magnificent in stru- 

 "ments so much in vogue, but with the 'object of dispelling a common 

 "impression widely prevalent, at least among those with whom I habitu- 

 "ally come into contact, that the kind of work such as I now put forth 

 "can be done only with the help of elaborate and expensive instru- 

 "ments." 2 



1 The cost of the Objective of l-4th inch focus and 170 aperture, made by Mr. 

 Tolles, of Boston, is 70 dollars (about 14); which would purchase a very good 

 English Student's Microscope, with a series of excellent Objectives up to ]-10th 

 * immersion. 



2 Now that the requirements of a Student's Microscope are so definitely under- 

 stood, the Author would suggest whether it woulti not be better that a new stand- 

 ard screw of much smaller size than the ' Society's ' should be adopted for it, so 

 as to enable Students' ' Objectives ' to be set in the small light ' mounts ' used on 

 the Continent, instead of in the massive mounts which the Socciety's screw neces- 

 sitates; especially as, on the construction already recommended ( 17) no adjust- 

 ment for thickness of covering-glass is required, even for high powers. A small 

 light ' nosepiece,' for change of Objectives, could then be added at a low cost, 

 to the great convenience of the worker. Such Microscopists as, commencing 

 with * Students' Microscopes,' afterwards provide themselves with more complete 

 instruments, would readily employ their Students' objectives with the latter by 

 means of an ' adapter.' But the Author's experience would lead him to recom- 

 mend any one engaged in research to keep his Student's Microscope, with its own 

 series of objectives, constantly on his table; and to have recourse to his larger 

 instrument, with its first-class Objectives and varied methods of Illumination, 

 only for the more complete scrutiny of the preparations he has made with his 

 simpler model. 



