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operate side by side together, through a medial rod and two 

 bent levers, upon a pinion on the axle of the index. The 

 pinion is driven by a T ratchet, set crosswise of the second 

 lever end. It is bent to an arc of about one and a-half inches 

 radius, and armed with forty minute teeth. The heel of this 

 lever is provided with adjusting screws to determine the pro- 

 portional motion of the index to the air-box lids. The index 

 point, outside, traverses the entire circuit of the dial-plate 

 during a rise or fall of tiuo mercurial inches, so that the half- 

 hundredth divisions on the dial-plate enable the topographer 

 to read altitudes of five feet, which he can subdivide by the 

 eye, after practice, into single feet. The instrument is made 

 with great nicety and beauty, and satisfies a want long felt 

 by practical field geologists. The accomplished maker con- 

 siders it thermo-compensating ; but Mr. Lesley's long expe- 

 rience with aneroids of various make and size, leads him to 

 believe that this beautiful instrument, so far in advance of any 

 other yet constructed, will prove no exception to the rule, that 

 it is necessary to provide for each instrument its own scale of 

 thermometric variation. The adjusting screws within, will 

 enable the observer to make the instrument conform either to 

 a mercurial standard reading half-hundredths of a mercurial 

 inch, — or to a hypsometric standard of a thousand feet. In the 

 former case, a proportional correction must be made of thou- 

 sandths of an inch to a foot ; in the latter case, the instru- 

 ment will, within a moderate range, make the correction itself. 

 To meet the difficulty of recording great altitudes (over two 

 thousand feet), Mr. Becker has applied an exterior adjust- 

 ment. A large set screw, marked with the barometric inches 

 on a small scale, projects below, and returns the index to the 

 place of commencement after that a great ascent or descent 

 has carried it round the circle. 



Prof. Cresson described the plans of Prof. Lowe, the aero- 

 naut, for crossing the Atlantic in thirty hours, by a balloon 

 of seven hundred thousand cubic feet capacity (using but four 

 hundred thousand), charged with city gas (of forty pounds to 

 the thousand feet ascensional power), and floating in the 

 highest, and therefore swiftest, northeastward moving strata 



