418 



SCIENCE 



[N. S. Vol. XL VI. No. 1191 



the right hand disc to be fastened in different 

 positions by the pin P. This arrangement 

 allows objects of considerable width to be 

 held by their edges. A supporting screw in 

 the movable disc opposite the groove is some- 

 times used to prevent tipping and wedging of 

 the disc under strong pressure, but it is gener- 

 ally not required. 



Universal Tripod Bases. — Of all laboratory 

 implements the tripod stand is probably the 

 one that is most constantly and universally 

 employed. A tripod base forms the founda- 

 tion of a great number of scientific instru- 

 ments; it is therefore desirable to have a 

 number of accurately made bases for use with 

 interchangeable apparatus, and adaptable to 

 a great variety of purposes. 



The ordinary way of fastening the stand- 

 ard to a tripod base is by means of a screw 

 on the end of the rod. This is permissible 

 when the rod is to be left in position perma- 

 nently, but when it has to be removed fre- 

 quently, it is very inconvenient, as a special 

 wrench is required for the operation. When 

 accurate construction is required it is nec- 

 essary to reduce the diameter of the lower end 

 of the standard to form a shoulder, and to 

 cut the screw in a lathe. This adds consider- 

 ably to the expense and difficulty of fitting 

 apparatus to the base. A much simpler and 

 better mode of attachment can be employed 

 which has proved itself to be very satisfactory 

 in m.y laboratory. The bases that I have 

 made are of two sizes. The larger one covers 

 a circle of 30 cm. and weighs 5 kilograms. 

 Its center is a cylinder 8 cm. in diameter and 

 7 cm. in height. This base is like that of the 

 large adjustable stand which I have described, 

 and is turned and bored on the lathe in ex- 

 actly the same manner as that. The central 

 hole has a diameter of 19 mm. and the stand- 

 ards are clamped in it by a large brass screw 

 which passes horizontally through the center 

 of the hub. As the screw has a large head 

 with four spokes like the hand-nut on the 

 universal clamp figured in the drawing, the 

 rods and bushings are held with the greatest 

 firmness, but they can be changed almost in- 

 stantly. This kind of attachment allows a 



certain amount of vertical movement of the 

 standard of a table, or of apparatus, when 

 variation of height is desirable. When a more 

 extensive elevation is necessary the tripod can 

 be placed over a hole in the table through 

 which the rod can pass, or it can be supported 

 on rods clamped by brass set-screws in 13 mm. 

 holes in the cylindrical feet. These supple- 

 mentary rods may be used as substitutes for 

 leveling-screws. If such screws are required 

 they are made with brass cylindrical nuts 

 which are clamped in the holes in the feet. 

 These holes are exactly at right angles to the 

 plane of the bottom of the feet, it is therefore 

 possible to have four vertical rods, parallel to 

 one another, attached to the same base. This 

 is a great convenience in assembling compli- 

 cated combinations of apparatus. Hods 

 smaller than the holes can be clamped by 

 means of bushings. When these bushings are 

 of non-conductors the rods can be insulated, 

 or the rods may be made of these materials. 



The smaller base has all the features of the 

 one just described, and weighs about three 

 fourths of a kilogram. The holes in the feet 

 are 10 mm. in diameter, and the central one 

 13 mm. These bases can be bored while 

 clamped together in pairs. This insures exact 

 correspondence of the holes when the bases are 

 used together in combinations. They form 

 excellent end supports for the horizontal rod 

 of an optical bench, or similar apparatus. 

 They may be used instead of flanges for table 

 tops and wheels. They can be fastened easily 

 to the wall or ceiling by screws passing 

 through the holes in the feet, or be em- 

 ployed in the construction of a wall bracket 

 of adjustable height. In order to make such 

 a bracket two short rods in two of the supple- 

 mentary holes are held in corresponding holes 

 in a block of wood screwed to the wall. A 

 long rod in the anterior leg terminates in a 

 rectangular piece through which passes a hor- 

 izontal rod abutting against the wall. A 

 table top is attached to the central standard 

 when an adjustment for height is desired, or 

 it may be screwed or clamped to the anterior 

 rod. Frederick W. Ellis 



MoNsoN, Mass. 



