Page:Popular Science Monthly Volume 91.djvu/790

 774

��Popular Science Monthly

�� ��A Jack to Keep Automobile Weight from Tires

A SIMPLE jack for lifting the wheels of an automobile from the floor, to keep the weight from the tires while it is standing in the garage, is shown in the accom- panying illustration. It is made of 2 by 5-in. material hinged together with strips of i-in. stock fastened to the lower block The lower block should be about 3 in. high and the second block should be long enough so that the combined length of the two will be about I in. longer than the distance from the underside of the hub to the floor. The method of hinging the blocks together and the manner of using them are clearly shown. It is necessary to build four of these, one for each wheel.-

��8

��An individual wheel jack to keep automobile weight from the tires

��-Abner B. Shaw, glass

��focusing glass to examine the image. The three-legged type with adjustable glass can be purchased at reasonable cost from almost any dealer, and is preferable.

Another way to do fine focusing is to get fine cover glasses used in mounting speci- mens for examination with a micro- scope and fasten them to the ground glass with Canada balsam. Since the balsam has the same index of refraction as glass, these fine spots will appear as clear glass. Now place the focusing glass partly over one of the cover glasses and focus on the surface of the ground glass, paying no attention to the image of the object to be photo- graphed. Now focus the image on the screen, examining it not on the ground glass but in the clear space of the cover The image being examined is within

���ne imaqe here

��Camera Focusing Screen for Fine Detail Work

WHEN the amateur photographer is confronted with the need of making a picture of an object in which the detail is very fine, he may find the ordinary focusing methods not sufficiently exact. At a slight expense, any camera with a ground glass focusing arrangement can be equipped with a superior focusing screen equaling those employed in high-class

p h o t o - m i - crography.

Take an unexposed plate having a single coated emulsion of the size used in the cam- era, and expose it for one second in the dark room to a candle at a distance of 10 ft. Developing and fixing in the usual way will yield a plate with a slight tint of gray. The emulsion with its exceedingly fine particles of silver thrown down makes a focusing screen of much finer grain than the surface of the ground glass which comes with the camera. The class of work which calls for this kind of screen requires a

��the clear glass and is not distorted by irregu- larities of surface, however small. Such exact methods can yield proper results only when the sensitive plate at the time of exposure is in exact register with the image obtained on the screen. — C. E. Drayer.

���Clear cover

lass fastened to ground qlass with Canada balsam

��Focusinq x qlass

Microscopic focusing through the clear places in a screen

��Lathe Centers Used as a Clamp for Gluing a Box

IN the absence of a clamp large enough to hold a box I desired to glue, I used the centers of my lathe as shown. The cone centers were removed and a faceplate used in both head and tailstock. The box was

��Box

��Wood block

���^

��The screw of the tailstock served the purpose of a carpenter's clamp for gluing the work

placed between these parts and the tail- stock screw tightened. This held the parts firmly together while the glue dried. It is necessary that a box have its sides and ends perfectly square for gluing in such a clamp, as the face-plate surfaces are perfectly true and will press the parts together in a straight line. — Joseph Purdy.

�� �