METEOROLOGICAL INSTRUMENTS. 



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from the lower part of the barometer scale, 

 which reaches to the surface of the mercury. 

 The scale is fastened to the case by four screws 

 passing through long holes covered by springs, 

 allowing the scale and point attached to be 

 moved up or down, and set at any time in exact 

 contact with the surface of the mercury, by a 

 brass knob near the centre of the scale. From 

 the end of the steel point the scale commences, 

 and is graduated to thirty-one inches, subdivid- 

 ed as usual, and having a vernier with index ; 

 the mounting consists of a neat mahogany case, 

 well polished. This is a valuable instrument 

 where it can be set up by a maker, but cannot 

 usually be transported without being put out 

 of order, requiring to be kept in a vertical po- 

 sition, but may be sent unfilled, and requires 

 but little skill to fill and immerse in the mercu- 

 ry, directions for which will be furnished. 



Price, $22.00. 



Marine Barometer. (Fig. 610.) The ba- 

 rometer is of great use to the manner, who is 

 thereby enabled to foresee and prepare for sud- 

 den changes of weather. The marine barome- 

 ter consists of a glass tube with reservoir of 

 mercurjr, as in the usual barometer, but having 

 a portion of the lower part con- 

 tracted to a very fine bore, to 

 prevent the unsteadiness of the 

 mercury, which would other- 

 wise be occasioned by the roll- 

 ing of the ship. The tube is 

 inclosed in a mahogany case, 

 square in front, and rounded 

 at the sides, and enlarged 

 somewhat at the upper end for 

 receiving the scales, for which 

 there is an opening with the 

 scales fixed on the sides, which 

 are graduated as in any other 

 barometers ; this opening is 

 covered by a small door, on the 



