APPENDIX. 921 



For use in very deep water a simple automatic starting and stopping 

 apparatus is placed inside the water-tight compartment of the cylinder, which 

 operates in such a way that while the instrument is descending or ascending 

 in water, the mechanism does not record the revolutions of the cylinder, but 

 only while it is at the depth at which the velocity is required. In this case 

 the spring is removed and one cord only is used. 



4O9b. Deep Sea Current Indicator. 



Benjamin Theophilus Moore, M.A. 



This instrument is intended to he used for the purpose of ascertaining the 

 direction of submarine currents. 



It consists mainly of a water-tight globular shell of gun metal pointed in 

 one direction, and terminating in the other in a long double vane, and is 

 carried by two pivots on a stirrup. Within the shell is a brass box, 

 suspended by giinballs in the manner of a ship's chronometer, and containing 

 a magnet with a graduated ring, and a train of clockwork. When the instru- 

 ment is lowered into deep water, its principal axis takes the direction of the 

 current, while the magnet settles itself in the magnetic meridian, after the 

 magnet and the instrument have taken up their respective positions, the 

 clockwork suddenly fixes the magnet at a known time. The instrument is 

 then drawn up out of the water and opened, when the fixed magnet shows 

 the direction, or bearing, of the current below. 



This bearing is shown directly by the instrument when it is suspended from 

 a fixed platform, or from a ship at anchor, or otherwise at rest. When the 

 ship is in motion, the instrument is to be used in combination with the deep 

 sea current meter, by which means the velocity and direction of the submarine 

 current can be determined simultaneously by a simple geometrical con- 

 struction. 



41 5b. Fare and Distance Indicator for Street Cabs. 



Robert Foster, Sunderland. 



This is an instrument for measuring the distance travelled by a cab or 

 other vehicle to which it may be attached. A driving band taking its motion 

 from the road wheel actuates counting wheels, and so pointers are made to 

 indicate on dials the distance passed over and the fare. There is also an 

 appliance for registering on a slip of paper all the fares taken during the day. 

 The pointers can be brought back to zero by the driver, but they cannot be 

 moved forward except by the motion of the vehicle. 



42 lc. Gravimeter. An instrument for the measurement of 

 the variations of the earth's attractive force, invented by J. A. 

 Broun, F.R.S., and constructed from his drawings by Dr. C. S. 

 Miiller, of Stuttgart. J. Allan Broun, F.R.S. 



The instrument consist of a weight suspended by two gold wires ; a single 

 wire fixed to the top of the weight and passing through its centre carries a 

 cylindrical lever ; when the lever is turned through 360 at the normal (say 

 southern) station the torsion of the single wire thus produced carries the 

 weight round through an angle of 90. The forces then in equilibrium are, 

 the torsion at force of the single wire and the attraction of the earth on the 

 weight, which, as the two wires are no longer vertical, has been slightly raised 

 and seeks to attain its lowest point. 



On proceeding from a southern to a more northerly station the earth's 

 attraction increases ; the amount of this increase which may be measured in two 

 ways : 



