REPORT OF ASSISTANT SECRETARY. 97 



cally safe from everything but malicious mischief. Special mounts are required in 

 order to increase the carrying capacity of the stage, and for transparent objects thb 

 stage must be perforated in order that the light may pass upward from the reflector 

 below. The instrument now in use in the Museum (Plate 2) was made in the year 

 1890, has been modified in a few details sinc(^, and has successfully endured manip- 

 ulation by thousands of inexpert hands — of children as well as adults — without 

 injury, and this without attendant supervision of any kind. 



For the purpose of exhibiting a series of preparations mounted in the usual way 

 upon glass slips or ''slides," an entirely difterent form of ajiparatus has been de- 

 vised (Plates 3 and 4). An indefinite number of slides — from 10 to 100 — are attached 

 to an endless band of linen by means of thin brass holders which allow the slides to 

 be changed when desired. This linen band passes over two rollers mounted upon a 

 light brass frame which occupies the place of the "stage" of an ordinary micro- 

 scope. The loops'of the band hang free. One of the rollers has a projecting pivot 

 with a milled head by means of which it may be rotated, and the two rollers are 

 connected by a narrow belt at each end. As the rollers are made to revolve, the 

 band carrying the slides passes horizontally under the microscope, resting mean- 

 while upon the two narrow belts and being kept at a definite distance from the 

 objective of the microscope by two guides, which press upon the slides from above. 

 The brass frame rests upon a grooved bed-plate which permits a lateral movement 

 of the frame. This lateral motion is controlled by a screw operated by means of a 

 second milled head in convenient proximity to the one giving the tu-and-fro motion. 

 As in the other instrument, tlie-siiecimens and nearly all parts of the mechanism are 

 inclosed in a box secured by a lock, the only exposed pai'ts being the microscope and 

 the two milled heads controlling the motion of the slides. The advantages of this 

 form of apparatus are that the usual glass slide, 3 inches long by 1 inch wide, 

 upon which microscopic objects are usually mounted, may be used, and especially 

 that the focal distance is not disturbed by difterences in thickness of the glass slides. 

 The only disadvantage is that the mechanism is somewhat more delicate and com- 

 plicated than in the other instrument and requires some little protection from the 

 thoughtless violence of curious children. Microscopes copied from the original here 

 described have been in use for several years, and no irremediable difficulties have 

 been found in the way of their perfectly successful operation. 



It is .safe to say, from present experience, that these methods of installation of 

 microscopic exhibits promise to open a new and interesting field of observation and 

 study to museum visitors. 



Physical apparatus. — Mr. W. 0. Winlock remains in charge of tliis 

 section as honorary curator. During the year there were deposited in 

 the Museum by the Smithsonian Institution twelve pieces of elec- 

 trical apparatus supposed to have been used by Professor Henry in his 

 laboratory work at the Institution; also sixteen photographs of early 

 electrical apparatus. These photographs were made under the direc- 

 tion of Miss Henry and were exhibited at the World's Columbian 

 Exposition in 1893. A number of pieces of apparatus were purchased 

 by the Smithsonian Institution and deposited in the Museum, includ- 

 ing a pocket dial with compass, five sand-glasses, a Japanese clock, 

 an iron clock dial, a hexagonal clock with three dials, and an hour- 

 glass. 



NAT MUS DO 7 



