244 ANNUAL KECOKD OF SCIENCE AND INDUSTRY, 



ELECTRICITY. 

 1. Magnetism. 



Sir William Thomson has presented a paper to the Royal 

 United Service Institution upon a new form of azimuth and 

 steering compass, with adjuncts for the complete application 

 of the principles of correction for iron ships suggested by the 

 Astronomer Royal. Hitherto, owing to the large size of the 

 needles in the marine compass, the method of correcting the 

 quadrantal error by placing masses of soft iron on the two 

 sides of the binnacle, suggested by Professor Airy, has been 

 practically unattainable. The new compass proposed de- 

 pends upon the principle discovered by the author, that stead- 

 iness can only be obtained by increasing the vibrational pe- 

 riod. It consists of a thin strong paper card supported on a 

 thin rim of aluminum, from which thirty-two silk threads or 

 fine copper wires pass to a central boss of aluminum, which 

 rests on the projecting lip of an inverted aluminum cup in 

 which a sapphire cap is mounted, the whole resting on an 

 iridium pivot. Eight small steel needles from 3^ to 2 inches 

 long, weighing 54 grains, are fixed, like the steps of a rope- 

 ladder, on two parallel silk threads, and slung from the alu- 

 minum rim by four fine copper wires through eyes in the 

 four ends of the outer pair of needles. The weight of the 

 central boss, aluminum cup, and sapphire cap is only five 

 grains. For the 10-inch compass the whole weight upon the 

 iridium point is about 180 grains. The period of vibration 

 of this card is about forty seconds. With this compass the 

 application of the principles of correction is easy and sure. 

 The paper also describes an adjustable deflector for com- 

 pletely determining the compass error when sights of the 

 heavenly bodies or compass marks on shore are not avail- 

 able, a new form of marine dipping-needle for facilitating 

 the correction of the heeling error, and the navigational 

 sounding-machine for taking soundings of 100 to 150 fath- 

 oms from a ship under full headway. 



Duter has presented to the French Physical Society mag- 

 nets obtained by subjecting circular steel plates to the action 

 of an electro-magnet terminated with a conical point applied 

 to the centre of the disk. In these magnets the neutral line is 



