402 Description of the Marine Transit. 



from the discharging aperture, can be uniformly maintained, 

 provided that changes of temperature have no etfect on the 

 result ; or, if they have, that the tjuantity of the deviation 

 may be estimated, and added or subtracted as the case may 

 require. 



A drawing, with a brief description, will best explain the 

 construction of the instrument, and the way in which it is 

 proposed to apply to |nactice the principle that has just 

 been slated. (See Piate X.) 



The f'gure is a perspective representation of the Marine 

 Transit, No. 1, complete, and pendent from the deck of 

 the ship. The iron magazine AA, containing a sufficiently 

 abundant but an indefinite quantity of pure mercury, is 

 arranged, like the steering compass, to swing in gimbals, 

 so that the parts attached to it I7iay at all times preserve a 

 vertical position. The regulator B, the graduated tube C, 

 and the gauee D, are of glass, connected by iron joints pppy 

 and furthtr strengthened by brass supporters iiii: jointed 

 brass rods fh^J'h, by which the globe JE swings, are also 

 fastened to the magazine. The waste pipe 7inn, and the 

 other tubes mmm, ooo, are made of the elastic gum, which 

 has been found to be impenetrable to air. 



In the bottom of the magazine, at the joint p, there is 

 an aperture conanunicating with the conduit k; il is rather 

 larger than the aperture; in the regulator 5; and as the 

 waste pipe continually carries off the excess of its volume, 

 there will be aK\ays the same depth of mercury maintained 

 in B to regulate the issue through ; into the gauge D. 



Experience will determine the must suitable substance 

 for mercury to run through. Trial will be made of ruby, 

 which it is apprehended has neither affinity to mercury, nor 

 will be liable to any sensible influence from tcn)perature 

 or friction. By the elevation or depression of the hollow" 

 screws in which the apertures are fixed, they receive their 

 necessary adjustments; the lower one j being set to fill the 

 gauge D in '21 hours, when the gauge and its contents are 

 at the temperature of 6a°. 



As it may be assumed that mercury expands uiiiformly 

 througiiout liio small range of temperature, to which the 

 interior of a ship is ever exposed ; (supi)osing this range to 

 be from 20^ to 1 10%) tables for immediate use have been 

 calculated on this principle, from data obligingly supplied 

 bv Mr. John Dalton, of Manchester, to show the contents, 

 and, consequently, the corresponding value in time of the 

 gauge "D, at every tenth of a degree of the thermometer. 

 This minute temperature is indicated by the thermometer M, 



wiiich 



