THE GUIDING-NEEDLE ON AN IRON SHIP. 295 



The Makiner's Compass. — To relate what is known or conject- 

 ured regarding the origin, history, and development of the com- 

 pass would not be pertinent to this article, and, besides, such infor- 

 mation is readily accessible in any encyclopaedia ; to impart in a 

 general way a knowledge of its construction is more to the point, 

 especially in view of the object of this paper, which is to treat of 

 the behavior of the instrument in an iron ship ; and this kind of 

 knowledge is neither easily obtained nor generally free enough 

 from technical terms to be readily intelligible to the non-profes- 

 sional reader. 



Like almost every other instrument, the compass has repre- 

 sentatives of many a type ; to explain the mechanical and mag- 

 netical principles of construction, however, in their general appli- 

 cation, it is necessary to have reference to some particular type, 

 and for this purpose I shall select the one that in my opinion is the 

 most trustworthy for steering a ship from her port of departure to 

 her haven of destination — the Ritchie liquid compass. This is 

 an American invention, Mr. E. S. Ritchie, of Boston, having many 

 years ago taken out a patent for a liquid compass to be used at 

 sea. From time to time it has been improved, until to-day, in the 

 seven-and-a-half -inch compass supplied our navy, is probably 

 realized the most accurate and complete instrument afloat. So 

 generally has the excellent workmanship of the manufacturer 

 been appreciated, that his compasses now guide the ships of many 

 a nation in every sea. In the wheel-house of the latest large float- 

 ing structure — the British steamship City of New York — will be 

 found a Ritchie liquid compass. 



The compass and its several parts are represented in Figs, 4 to 7, 

 and the reference-letters in every instance pertain to the same 

 parts : JE' is a copper bowl, with two short arms, D, D (one 

 only being visible), which rest in the grooves of an outer ring,jB; 

 this, in turn, has two short arms, C, C, which repose in the 

 sockets of the binnacle, as the case for holding the compass on a 

 ship is called. This method of suspension, termed gimbals, allows 

 the bowl to swing freely in two planes, so that really it partakes 

 but little of the rolling and pitching motion of the ship. A slender 

 brass spindle known as the pivot (P, Figs. 4 and 7) is screwed into 

 the bottom of the bowl, and on it rests the card. The bowl is 

 filled with a liquid composed of nearly equal parts of pure alcohol 

 and distilled water, and is hermetically sealed with a plane glass 

 cover, which permits the card to be distinctly seen without dis- 

 tortion. The card (Fig. 6) consists of an outer rim {M), a central 

 bulb {K), and four tubes, H, H, H, H—?^\\ made of very thin 

 sheet-brass. The rim has double curvature — circular around the 

 pivot, and semi-cylindrical from the inner to the outer edge, as 

 shown in section in Fig. 5. The card is painted white, and has 



