OF SUEVEYING INSTEUMENTS. 71 



FIG. 513. FIG. 521. 



516. Opiesometer, or Pocket Perambulator, for measuring curved lines on maps, etc. 



3s. 6d. and 4s. 6d. 



517. Trocheameter, for registering the revolutions of a carriage wheel, and thereby 



determining the distance travelled ; applicable also for counting the rotations 

 of machinery with certainty, however high the velocity. (See also engine 

 counters and steam gauges) . . . . . 2 10 



518. Current Meter, for showing the rate of flow of tide in any stream or river, 



and the amount in gallons per hour flowing off (fig. 518) p. 72 5 10 



519. CUEBENT METEE (DOUBLE), in case 7 inch, by 2 inch., circuit representing twelve 



miles ; answering also for ascertaining the rate of a ship's speed 6 10 



520. TIDE GAUGE (SELF-EECOEDING) (fig. 72), p. 24, for showing the rise and fall of 



water in rivers, canals, locks, or any bodies of water, the rate of evaporation, 

 etc., showing the exact time at which any increase or reduction may have 

 occurred ; see also No. 72 . . . . . 32 



521. Pocket Altazimuth, Casella's, for travellers and military surveys, improved and 



modified by the kind assistance of Francis Galton, Esq., F.E.S. Altitudes, 

 azimuths, compass-bearings, clinometric degrees and levels, are all obtainable 

 by this strong and handy, but accurate little instrument, whose diameter 

 is 2 inches, thickness 1^ inch., and weight 5^ oz. The advantages of its 9 

 use have been so increased by the recent addition of an excellent telescope, 

 as to make it really perfect for the various purposes to which it can be 

 applied (fig. 521) ... ..550 



LAND CHAINS. 



522. Land Chains, best machine made, Government pattern, with three sawn oval 



connecting rings, brass swivel handles, and usual marks. Two pole, 5s. ; fifty 

 feet, 5s. 6d. ; Gunter's four pole, or sixty-six feet, 7s. 6d. ; one hundred feet, 8s r 



523. LAND CHAINS, same pattern as above, rather lighter, 6d. to Is. each less, or with 



only two intervening oval rings, Is. to 2s. each less. 



524 . LAND CHAINS, machine made, of best steel wire, hardened, tempered, and japanned 



with three sawn oval connecting rings, best swivel handles and marks, two 

 pole, 7s. ; fifty feet, 7s. 6d. ; Gunter's four pole, or sixty-six feet, 13s. ; one 

 hundred feet, 14s. 



Strong, light, and very convenient. 



