THE GYROSCOPE FOR MARINE PURPOSES. 153 



believed that the gyro-steadying plant of the active type will be well within 

 practical limits of space, weight and cost. Especially is this true when 

 compared with the practical results of its operation. A great many ships 

 as they now stand could with profit utilize the gyro-steadying gear of this 

 class, which is at present available, and some important installations are 

 now being contemplated. In this connection it is interesting to note that 

 the weight of an active gyroscope for each degree of roll-quenching power 

 on a modern battleship would be about one-tenth that of the submerged 

 armor displaced, and cost much less, this being outside of the very impor- 

 tant consideration of having the entire ship under control either auto- 

 matically to extinguish roll or at the will of the commander with its many 

 evident advantages. 



Referring to the use of the gyroscope as a compass, it is interesting 

 to note that the possibility w^as first brought out in 1852 by Foucoult, 

 who, after many attempts, succeeded finally in making up an apparatus 

 so delicate and beautifully constructed as to demonstrate the working of 

 the instrument in the short period of duration of spins of a small disc, 

 the observations being taken through a telescope, the directive factor being 

 only a fraction of that of the magnetic needle. With this difference, how- 

 ever, that magnetism or the location and variations in the positions of the 

 magnetic meridian have nothing whatever to do with its directive feature, 

 and, in fact, it points to exact geographical north, not to magnetic north. 



About this time Foucoult took this apparatus to England and there 

 aroused the greatest enthusiasm in scientific circles by exhibiting it in 

 operation to the Royal Society. Hopkins in America, associated with the 

 "Scientific American," in 1878 made a small electrically driven gyroscope by 

 means of which better and more persistent results were obtained. More 

 recently, attempts have been made by a German firm to use mercury floats 

 for sustaining therotating wheel constituting a gyrostat which, in this instance, 

 runs at the enormous speed of between 22,000 and 23,000 revolutions per 

 minute, which has been considered by many to be impracticable. Those 

 familiar with the use of mercury in its mechanical and also electrical applica- 

 tionsusually find it very unsatisfactory. At best it is a volatile liquid, sub- 

 ject to many changes with differences in temperature, and, which is worse, 

 is also subject to the phenomenon known as "sickening" which effects the 

 surface and the mercury, and for some distance under the surface, altering its 

 mechanical behavior and also its viscosity. The best engineering practice 

 has for some years avoided mercury, drawing away from its use in every pos- 

 sible way, and especially where electrical connections were involved, and 

 substituting, in its stead, simple mechanical methods which are free from 

 these serious objections. Working in this line I have found simple detail 



