Mechanical Science. 195 



The immense body of light condensed together by it gives a won- 

 derful richness and vivacity of colouring to the image wliich, com- 

 bined with its sharply-defined outline and vast dilatation, distends 

 the faculties with surprise and pleasure, frequently surpassing the 

 most lively anticipation. 



Upon the whole there would be nothing to wish for or to find 

 fault with about Mr. C.'s instrument if it possessed aplanatic object- 

 glasses of sufficiently short foci to developethe tissue of animalcules 

 and other regular microscopic objects. Nothing certainly can 

 exceed the perfection of its combined double treble achromatic, the 

 power of which is also admirably adapted for exhibiting large 

 popular objects, but far too low to show those curious and difficult 

 minutia which gratify a connoisseur. Such an objective as that 

 famous deep sextuple one lately worked by Mr. W. TuUey, which 

 demonstrates the most difficult test objects with such incomparable 

 facility, would complete the effectiveness of this really respectable 

 and scientific engine of public instruction and amusement. This 

 deficiency is shortly to be supplied. 



3. Improvement in the Barometer. — An improvement has been 

 made in the barometer of Gay-Lussac by M. Bunten, which has been 

 submitted to, and received the approbation of, the Academy of Sciences 

 at Paris. Its object is to prevent the introduction of bubbles of 

 air, which almost inevitably takes place when the barometer is carried 

 either on foot or horseback, or in a carriage, in a horizontal posi- 

 tion. It consists in expanding the glass in one part of the wide 

 tube, so as to form it into a chamber, from the centre of which a 

 capillary tube of a certain length descends perpendicularly, by which 

 the mercury must necessarily pass, either when rising or falling. 

 If a bubble of air enters, it necessarily moves up by the surface of 

 the large tube, and is stopped at the top of the chamber, producing 

 no error in the observation made whilst it is there. When the 

 barometer is inverted the bubble escapes of itself. This invention, 

 the reporters observe, does away with the only inconvenience attend- 

 ing the use of Gay-Lussac's barometers, without adding anything 

 to their fragility. — Revue Ency. xxxviii. 536. 



4. Effect of the Moon upon Barometric Pressure. — M. Flauger- 

 gues has added his efforts to those of the persons who have endea- 

 voured to ascertain the effect of the moon's attraction upon the 

 atmosphere of our globe, endeavouring to elucidate the subject by a 

 very close and continued series of barometrical observations made 

 daily at mid-day since 1808. The column of mercury in the baro- 

 meter was 2.46 lines in diameter, and in the cistern 37.89 lines in 

 diameter. The height was marked off" to the -j^^th of a line, and 

 corrections made for capillarity, variations of the external level, 

 temperature of the mercury both in the tube and in the cistern. 

 The following is the table of the mean height of the mercury drawn 



2 



