154 ANNUAL OF SCIENTIFIC DISCOVERY. 



elevations, and vice versa, forming a curious illusion ; for instance, a 

 metal spherule may appear like a glass ball silvered on the under side, 

 and the margin of a wafer may seem to ascend from the water into the 

 air. 



With this instrument the microscopic dissecting knife can be 

 exactly guided. The watchmaker and artist can work under the 

 binocular eye-glass with certainty and satisfaction. In looking at 

 microscopic animal tissues, the single eye may perhaps behold a con- 

 fused amorphous, or nebulous mass, which the pair of eyes instantly 

 shape into delicate superimposed membranes, with intervening spaces, 

 the thickness of which can be correctly estimated. Blood corpuscles, 

 usually seen as flat discs, loom out as oblate spheroids. Prof. R. 

 asserted, in short, that the whole microscopic world could thus be 

 exhibited in a new light, acquiring a ten-fold greater interest, display- 

 ing in every phase, a perfection of beauty and symmetry indescri- 

 bable." 



GIGANTIC TELESCOPE. 



A NEW and gigantic telescope, rivalling that constructed by Lord 

 Rosse, is now erecting upon Wands worth Common, by Mr. Gravatt, 

 for the Rev. Mr. Craig. It consists of a plain tower, with a long tube 

 slung at its side. The tower, consisting of brick, is 64 feet in height, 

 15 feet in diameter. Every precaution has been taken in the con- 

 struction of this building, to prevent the slightest vibration ; but, if 

 any disappointment in this respect should arise, additional weight can 

 be obtained by loading the several floors, and the most perfect steadi- 

 ness will be thus insured. By the side of this sustaining tower hangs 

 the telescope. The length of the main tube, which is shaped some- 

 what like a cigar, is 76 feet; but with an eye-piece at the narrow 

 end, and a dew-cap at the other, the total length in use will be 85 

 feet. The design of the dew-cap is to prevent obscuration by the 

 condensation of moisture which takes. place during the night, when 

 the instrument is most in use. Its exterior is of bright metal, the 

 interior is painted black. The focal distance will vary from 76 to 85 

 feet. The tube at its greatest circumference measures 13 feet, and 

 this part is about 2-4 feet from the object-glass. The determination of 

 this point was the result of repeated experiments and minute and 

 careful calculations. It was essential to the object in view that there 

 should not be the slightest vibration in the instrument. Mr. Gravatt, 

 reasoning from analogy, applied the principle of harmonic progression 

 to the perfecting of an instrument for extending the range of vision, 

 and thus aiding astronomic research. By his improvements, the 

 vibration at one emj of the tube is neutralized by that at the other, 

 and the result is, that the utmost steadiness and precision are attained. 

 The ironwork of the tube was manufactured by Messrs. Rennie, 

 under the direction of Mr. Gravatt. The object-glasses are also of 

 English construction, and throw a curious light on the manner in 

 which an enlightened commercial policy has reacted upon and pro- 



