III. MISCELLANEOUS. 639 



advantage that any wearing that may be produced by the screws may be at 

 once corrected without the aid of the mechanician. The instrument is particu- 

 larly adapted for levellings of precision ; that now exhibited was employed in 

 this way in the European measurement of a- degree by Prof. Spangenberg. 



3127. Instrument for the Construction of Altitude 

 Curves. Bau Deputation, Hamburg. 



3127. Variable Scale. 



This instrument, which was invented by IT. H. Reitz, facilitates plotting a 

 point on a contour line from the two nearest points, the altitudes of which 

 are determined. See 3217a. 



3128. Plan 1 : 20,000 in frame under glass. 



3128a. Hamburg and its Environs, scale 1 : 20,000, en- 

 graved by H. Fetters. Bau Deputation, Hamburg. 



3129. Plan 1 : 4,000 in frame under glass. 



Bau Deputation, Hamburg. 



3129a. Plan of Hamburg and its Environs, Official 

 edition. According to the land survey, &c., engraved by S. Sie- 

 bert ; scale 1 : 4.000. , Bau Deputation, Hamburg. 



3130. Photograph of a Circle of Altitude, objective of 

 21'" aperture, diameter of circle 10". Latest construction of the 

 instruments of a similar kind extensively in use in Russia for 

 determining geographical localities. 



A. Repsold and Sons, Hamburg. 



3131. Paugger's Patent Dromoscope. 



This dromoscope is circular, and has almost the shape of the ordinary 

 chronometer. 



Its diameter is about 22 centimeters, and its height (thickness) 7 centi- 

 meters. On the upper part there is a fixed compass card, with two hands, 

 besides a graduation running to 45 degrees to the right and left, which lies 

 below these hands (scale of deviation and variation). The inner mechanism 

 of the instrument is a perfect calculating machine ; it exhibits for any desired 

 course the exact tangent formula of the deviation of the compass when the 

 contrivance for turning it has been put in motion. On the lower or back 

 part of the instrument there are five scales or graduations marked A, B, C, 

 D, and E ; and corresponding with these graduations are five set screws 

 (not visible in the photograph) . With these adjusting screws, and the scales 

 belonging to them, the five co-efficients of deviation for any ship can be 

 indicated. 



By means of this instrument the deviation of the compass, either of the 

 course or azimuth, is indicated merely by stopping the hand. 



A printed description accompanies the instrument. 



3132. Pendulum Apparatus. Great Trigonometrical Sur- 

 vey of India. 



Kew Committee of the Royal Society, Kew Observatory. 



