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. 



