196 



THE AMERICAN MONTHLY 



[October, 



forms, ranging from the rhizopods 

 even up to the vertebrates. 



The work done in making these 

 drawings and observations was very 

 great, for it has been calculated that 

 the 605 drawings on the chart re- 

 quired the examination of a quarter 

 of a million different specimens under 

 the microscope. During the home- 

 ward voyage of the "Rodney" up- 

 wards of 1300 drawings were made, 

 and on the " Sylvia "' five hundred. 



A Simple Eye-piece Micrometer. 

 — Mr, W. M. Bale describes a simple 

 form of eye-piece micrometer, which 

 seems worthy of adoption by amateurs 

 who enjoy using home-made apparatus. 

 Judging from the description we would 

 recommend it as both accurate and 

 convenient, and it seems to possess 

 qualities for practical use which com- 

 mend it to the favorable notice of pro- 

 fessional observers. It consists of 

 two or more delicate fibres of silk 

 stretched across the diaphragm of the 

 ocular. It will require but little de- 

 scription to enable a person of ordinary 

 ingenuity to construct one. Remove 

 the field-lens of the ocular and apply 

 a very little stiff balsam to the under 

 side of the diaphragm at two points 

 diametrically opposite. Ravel out a 

 very fine, straight fibre of silk from a 

 ribbon — the transverse fibres of a 

 corded ribbon will serve very well. 

 Attach one end of the fibre to the 

 diaphragm by placing it in the balsam, 

 and stretch it across to the other side. 

 Be sure the thread is smooth and 

 straight. When it is so, a second 

 thread must be laid parallel to it, in 

 the same way. The difficulty now 

 met with is to get the two threads 

 parallel and at the right distance 

 apart. This is accomplished by plac- 

 ing a stage-micrometer upon the stage 

 of the microscope, and adjusting the 

 fibres until they correspond with the 

 lines on the micrometer. Suppose the 

 stage micrometer is ruled in thou- 

 sandths of an inch. If the lines in the 

 eye-piece exactly correspond, they 



will measure thousandths of an inch 

 with the objective used. If they do 

 not exactly correspond, they may be 

 made to do so by moving the draw- 

 tube out or in. Then mark the proper 

 position of the draw-tube, and there 

 will be no further use for the stage 

 micrometer except to detect any ac- 

 cidental change in the position of the 

 fibres. It is recommended that the 

 fibres be secured by strips of gummed 

 paper in addition to the balsam. It 

 is well to have these fibres, equally 

 spaced, and to adjust them to measure 

 thousandths of an inch, or else 

 micras (.001 mm.), with a ^ or -^ inch 

 objective. 



It seems not improbable that mi- 

 crometers made in this way will be 

 found to possess advantages over 

 simple rulings on glass. They do not 

 interfere with the optical pertection 

 of the eye-piece, and if the fibres are 

 accurately placed, so as to be quite 

 parallel, they will prove in every way 

 satisfactory. If any of our readers 

 construct such micrometers, we would 

 be pleased if they would make known 

 their experience with them through 



the JOURNAL. 



A Printer's Blunder. — In the 

 August number of the Journal the 

 printer has made a most annoying 

 blunder. On page 149 begins a por- 

 tion of an article referring to the 

 Fisheries Exhibition in London, and 

 having no connection whatever with 

 the preceding J matter. The Editor 

 can only express regret that such a 

 blunder should have been made. 



The American Association. — 

 The meeting at Minneapolis this 

 year seems to have been rather poorly 

 attended, and in consequence not 

 much was done in the section of 

 microscopy and histology. The Vice- 

 President, the Hon. J. D. Cox, pre- 

 sided, and Mr. Walmsley was made 

 Secretary pro tern, in the absence of 

 Dr. Carl Seller, We have no reports 

 of microscopical papers presented be- 



