Page:Popular Science Monthly Volume 91.djvu/45

 Popular Science Monthly

��29

��Dickory, Dickory, Dock, the Mouse Ran up the — Clock

WHERE are the creepy spiders, the mechanical beetles, and the spring- operated bugs which used to be the delight of the office boys and the terror of the stenographers? And surely the mouse has lost none of its effectiveness as a scream- producer.

A Frenchman has devised a magic wand with a celluloid mouse attached which is capable of great activity. It is worked by the action of a concealed magnet, so that the mouse appears to run up or down the wand in a mysterious way. The wand is a square tube of light wood covered with silk. The celluloid mouse has a small piece of iron on the bottom which is attracted by the magnet. When the wand is turned up a small lead weight on an endless cord falls and draws along the magnet which, in turn, takes the mouse with it. When the rod is tipped the mouse climbs up real- istically.

In the photograph the silk covering of the wand is broken away to show the interior mechanism.

���'CELLULOID MOUSE -MAGNET

��-wi[[k tubecovered

��The celluloid mouse runs up the rod by magnetic attraction

��These Magnifying Glasses Are Worn Like Spectacles

THE field of usefulness of the binocular magnifier, shown in the illustration on the right, in- cludes the scientific laboratory, the medical office or hospital, and the workrooms of botan- ists, metal workers, watch- makers, etc. An elastic headband fastens it on so that both hands are free. The eye-pieces of vul- canite are fitted with lenses in such a way that the fields of view are brought within small divergent angles.

A small incandescent lamp fitted with a reflector and condensing lens may be fast- ened over the top, current being supplied from a bat- tery carried in the pocket.

���Both eyes are used with this glass, so that the object exam- ined is seen in natural perspective

��Why You Can't Compare Ships According to Tonnage

THE different uses of tonnage terms when speaking of ships are causes of confusion to the lay mind. For ex- ample, steamship companies in order to impress upon the traveling public the size, and conse- quent relative safety of their craft, will advertise the sail- ing of a certain steamer of twenty-thousand tons, mean- ing, of course, gross tons. The company's agent, in en- tering her at the custom house, will take great precaution to certify that she is of only 7,340 tons, when paying tonnage taxes. He then is referring to her net tonnage, and in fact that stand- ard is used only when paying dues or taxes.

Displacement tonnage is al- most exclusively applied to war- ships as they do not carry cargoes. Strange to say, the tonnage of a battleship varies almost hourly, as coal or other weighty objects are used or taken on board. The tonnage of war- ships is, however, fixed ; they are referred to in terms of the fixed tonnage. A statement that a ten-thousand ton battleship sank a ten-thousand ton mer- chant ship does not mean that the ships were of equal size. The merchant ship would be much the larger owing to the different meanings of the term "ton," as applied to the two types of vessels. It is absolutely impossible to give rules for the relations of these terms, as the conditions vary too greatly. Generally speaking, the gross ton- nage of a ship is from fifty to one hundred per cent greater than the net tonnage. Tons dis- placement are always in excess of tons gross ; dead- weight tonnage is on an average from thirty to fifty per cent greater than gross tonnage. — Capt. C. A. McAllister, Engineer-in- Chief, U. S. Coast Guard.

�� �