i6 



THE AMERICAN MONTHLY 



[January, 



images of minute objects upon a 

 screen, so as to make them visible to 

 a large audience, he meets with a diffi- 

 culty which thus far has not been 

 satisfactorily overcome, viz., a great 

 loss of light. With low-power object- 

 ives the larger objects, such as whole 

 insects, sections of large-celled plants, 

 entomostraca, etc., can be shown fairly 

 well ; but when higher powers are em- 

 ployed the result is very disappointing. 

 We have seen the blood corpuscles 

 coursing through the vessels in a frog's 

 foot depicted on a screen in a large 

 hall, so that they could be distinguished 

 at a distance of several feet, but such 

 demonstrations are not. very striking,- 

 and it is not possible to make them 

 satisfactory before a large audience. 

 The principal difficulty is to obtain 

 sufficient light. The projecting mi- 

 croscope has not been perfected. No 

 doubt it is capable of doing much 

 more than it can do in its present form ; 

 and there seems to be an excellent 

 opportunity now for some ingenious 

 optician to devise a better one. 



The purport of this article is not 

 to suggest a new form, but we may 

 incidentally remark that the improve- 

 ments to be made are mainly in the 

 apparatus for condensing the light 

 upon the object. Specially construct- 

 ed objectives will doubtless be de- 

 manded after a while, but good low- 

 powers for the purpose can be selected 

 from among those now in use. We* 

 have yet to see a really good appara- 

 tus for condensing the light upon the 

 object. The problem offered to the 

 optician does not seem to be a difficult 

 one, and it is strange that it has not 

 been solved ere this. 



For the present it is useless to con- 

 sider the advantages of a projecting 

 microscope for purposes of instruction 

 in large halls, but we have long held 

 the opinion that it would be of great 

 assistance to professors in medical 

 colleges, while lecturing before small 

 classes, and also to other teachers, if 

 a projecting microscope could be de- 

 vised, giving a field of only two, or at 

 the most three feet in diameter, but 



showing very minute details of struc- 

 ture clearly and well illuminated with 

 high powers. Such an instrument 

 would surely be of very great assist- 

 ance to the teacher of animal or veg- 

 etal histology ; for he could point out 

 the details of structure, and designate 

 particular features of the specimen so 

 that there could be no misapprehen- 

 sion as to the structure referred to. 

 Such demonstrations would be far 

 preferable to the use of drawings and 

 photographs, and even better than the 

 examination of the specimen by each 

 student in the ordinary way, under the 

 microscope, for then there is always 

 some uncertainty whether the student 

 sees just what it is desired he should 

 see. If the lecturer could show the 

 specimens by means of the projecting 

 microscope, and thus have them before 

 his class while describing them, it cer- 

 tainly would be a great advantage. 



We are confident that it is entirely 

 practicable to do this. It remains to 

 be seen who will undertake the con- 

 struction of the proper instrument. 



NOTES. 



— We have received an excellent 5x8 

 photograph of Dr. William B. Carpenter, 

 taken, while he was visiting this city, by 

 A. Bogardus. As many of our readers 

 would, doubtless, be pleased to obtain 

 copies of this picture, we take pleasure 

 in saying that they can obtain them, for 

 50c. each, by applying to Mr. Bogardus, 

 at 872 Broadway. 



— A very excellent address was recently 

 delivered before the Postal Microscop- 

 ical Society (London) by the President, 

 Mr. Arthur Hammond. The subject was 

 " The Structure and Economy of the 

 Daphnia," a subject well chosen and well 

 treated. The entire address is published 

 in the Society's Journal of December, 

 1882, illustrated with two plates. It is 

 well worth reading by microscopists who 

 desire to know more about the common 

 daphnia than is to be learned from the 

 text-books. 



— Dr. Allen Y. Moore prepares slides 

 of crystals in this way : a cold, saturated 

 solution of the salt is made, which is 



