1869.] 359 [Hagen. 



exceptional cases of seven hundred and fifty diameters. For histologi- 

 cal purposes higher amplifications are necessaiy, but the physician 

 and the naturalist Avill usually be contented with a good amplification 

 of nearly three hundred diameters. 



Every possessor of a microscope wishes to test the power of his 

 instrument, but it is not, and never has been, my purpose to provoke 

 competition between American and PJuropean microscopes. Certainly 

 every step toward the perfection of the microscope is important, but 

 when the improvements are so minute that they cannot be used and 

 seen easily and everywhere, they are, I think, more interesting to the 

 artificer than to the operator. 



Indeed all over the world, first class microscopes have resolved the 

 14th, or even the 15th band of Nobert's test plates, — but should it be 

 found that American microscojies. even with a ^ in. objective, have re- 

 solved perfectly the 19th band, the superiority of these instruments 

 would be so enormous that it could easily be proved in any place and 

 at any time. 



I wrote to Mr. Hartnack to send me a first class microscope for 

 investigations in anatomy and natural history, and added that I in- 

 tended to compare it carefully with the best American instruments. 

 I did not fix the price, and left the choice entirely to him. 



He has sent the instrument marked in his catalogue as No. VIII, a 

 new small model, only difiering from his great model by wanting the 

 rack motion of the tube, by having but three eye-pieces, and by lack- 

 ing two objectives of lower jDower. 



The catalogue states that this new model, Hartnack's patent, dif- 

 fers materially in the optical and mechanical construction from his 

 old Oberhauser microscope. I confess I have been unable to discover 

 any difference, except that the fine moving screw is placed near the 

 top of the tube instead of below. The sliding tube to be elongated 

 by another tube has a diaphragm, which is also above the objective. 

 The diaphragm under the stage may be removed by a sliding ap- 

 paratus or by a sliding tube. The three eye-pieces, as in the Ober- 

 hauser instruments, have a low power, 21, 3^, 51 nearly. The 

 objectives are No. IV, ^ in.. No. VII,^ in., and No. IX, j^^^in., fitted 

 for correction for the cover-glasses, and for immersion. Hartnack 

 calculates the amplification for the first ranges from 70 to 480 Avith 

 the lower eye-piece, and from 140 to 950 Avith the strongest. The 

 camera lucida used Avith a fourth eye-piece, goes up to 1000 times. 

 The loAvest eye-piece has a glass micrometer. 



