V. MAPS, ETC. 653 



3151o. Mica-plates for uncoloured Compass Cards. 



Max. Raphael, Breslau. 



For the manufacture of compass cards, mica is now exclusively used. The 

 advantage to be derived from its use consists in the greater facility with 

 which the magnetic needle can he fixed, the transparency of the card, its 

 non-conductivity for electricity, its lightness and indifference to ordinary 

 changes of temperature, its durability, &c. 



315 lp. Compass, Hart's. M. Breguet, Paris. 



3151q. Patent True Course Finder. W. H. Roberts. 



The object of this instrument is to avoid arithmetical calculation in finding 

 the true course from the compass or magnetic course, with corrections for 

 lee-way, deviation, and variation. This instrument will give by three move- 

 ments of the index the true course to fifteen minutes. The outer rim of the 

 dial is accurately divided into degrees, and the inner rim into points, points, 

 and ^ points. The index has two arcs, A and B, and moves freely on a 

 pivot, C. The arc A indicates the points, 4 points, and points. The arc 

 B is so made that its centre line will point to the exact number of degrees 

 which are contained in the number of points shown by the arc A. The arc B 

 has also a vernier, by which the observer can read off to ^ of a degree. On 

 the extreme inner rim are arrows, half encircling the dial, to remind the 

 observer in which direction to allow easterly and westerly deviation and 

 variation. 



3151x. Chinese Compass. Ministry of Marine, Madrid. 



This differs from those employed by other nations, in the inversion of the 

 meridian line. 



3151y. A Compass or Azimuthal Needle, which was 

 employed in making the plans of the coast. This instrument was 

 made at Carthagena, at the end of the last century. 



Ministry of Marine, Madrid. 



3151z. Compass made at Carthagena, Spain, according 

 to the plan adopted by Don Antoino Doral, the Commander of 

 Fleet. Ministry of Marine, Madrid. 



V. MAPS, BOOKS, &c. 



COLLECTION OF MAPS, Ac., LENT BY THE ORD- 

 NANCE SURVEY. MAJOR-GENERAL CAMERON, 

 R.E., C.B., F.R.S., DIRECTOR-GENERAL. 



MOUNTED MAP of part of the city of WINCHESTER, scale 3^, or 

 1O56 feet to one mile, with corresponding photographic reduction 

 on -^Q scale from MS. plan. 



MOUNTED MAP of part of LONDON, scale 5 feet to one mile. 



