REPORT OF ASSISTANT ^iECRETARY. 31 



Tlie ordinary lighter type of exhibition case is not provided with 

 independent rollers, but can be raised by wooden trucks Avith rubber 

 tires about 4h inches in diamet<n', and movable in every direction, like 

 furniture castors. There is an attachment of levers so accnrately 

 adjusted that a case full of bottles can be moved from one end of the 

 building- to the other without disturbing labels or specimens. 



This system of tracks has been found of the greatest service in the 

 exposition work, in which the Museum is often called upon to take part, 

 since the cases can be arranged in cold or bad weather in sheltered, 

 warm rooms, and carried to their places on the floor. 



Another form of case especiall}^ advantageous for exhibition work 

 is what is called the "knockdown" case, in which the parts are fast- 

 ened together by pins and escutcheons. These cases have all the per- 

 manence and strength of fixed cases, and can be put together and 

 taken apart with great celerity. 



MOUNTINGS FOR INDIVIDUAL SPECIMENS. 



One of the most convenient and ingenious devices is that invented 

 by Prof. Merrill for placing geological specimens, jars, and other similar 

 objects upon sloping shelves, in such a manner that both specimen and 

 label shall be easily seen, while at the same time resting on a level 

 surface; the objects are not in danger of sliding forward. This system 

 is shown in the accompanying illnstration. (Fig. 5.) 



In the plate referred- to (PI. lU) the appearance of a number of speci- 

 mens thus arranged uiion the shelves is shown, though not well. The 

 arrangement of this case is in many respects one of the most satisfac- 

 tory pieces of installation which has ever been effected in the National 

 Museum. 



Each block or tablet has tacked to its front a small strip of tin, so 

 bent as to receive and hold the label and to allow its ready removal 

 when desired. This is painted the same color as the block, and is 

 thereby rendered quite inconsi^icuous. To prevent the sliding of the 

 specimens of the front row, which, in order to bring them below the 

 level of those in the back row, are without blocks, a continuous strip 

 of tin is tacked along the front edge of the shelf, bent as shown in the 

 cut. The full width of the strip is the average width of the labels. In 

 this series it is about one inch. The elevation of the back edge, which 

 is to check the sliding of the specimens, is from one-eighth to one-fourth 

 inch, while the front edge is folded over just sufficient to hold the label 

 in i)lace, as before. 



Among the other devices which have recently been adopted in the 

 department of geology two may be mentioned: 



The first is the curator's plan for showing the appearance of a cave by 

 setting up in its natural position a miniature grotto, with diminutive 

 stalactites and stalagmites, which he was so fortunate as to secure from 

 the Marengo Cave, in Indiana (PI. 11), placing at the sides of the 



