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A UNIVERSAL METEOROGRAPH, 



As regards temperature, any of the instruments may be used which 

 depend upon the expansion of solid bodies, so as to afford the means of 

 moving a lever. Such are Breguet's thermometer, Secchi's thermo- 

 graph — founded on the linear expansion of a copper rod, and Dr. Krecke's 

 metallic thermometer — founded on the different rates of expansion of zinc 

 and glass.* The air thermometer may also be employed, the lever being 

 actuated by a float on the surface of the mercury in the manometer. 

 The ordinary mercurial thermometer alone is inadmissible here.t 



* As, to my knowledge, Krecke's metallic thermometer has never heen descrihed, 

 and as it deserves a more general use in meteor- 

 ological observatories, on account of its simplic- 

 ity, accuracy, and ready adaptation to automatic 

 registry, I give here the principle of its construc- 

 tion. 



Two glass tubes, o o (Fig. I), about 5 feet long 

 and 1 inch in diameter, have their ends closed 

 with two iron plates, A and B, the lower one, B, 

 being fastened firmly to a wall, while the other is 

 so attached to the wall as to permit a slight dis- 

 placement. To the piece A is connected a zinc 

 bar, C C, and to the piece B a similar bar, D D'. 

 These bars are otherwise entirely free throughout 

 the rest of their length, but, in order to prevent 

 them from bending, a ring is placed near the free 

 end of each, so as to slip without sensible friction 

 on the glass tubes o o. In order that the zinc 

 bars may quickly assume the temperature of the 

 air they must not be too thick, and yet they 

 must have sufficient rigidity, which is secured by 

 making them trough-shaped. At the free end of 

 the bar D D' a steel support, p, is fixed, against 

 which rests the brass lever R M, somewhat like 

 the arm of a balance. The arms D' M and D' R 

 of this lever are unequal, and there is a movable 

 counterpoise, R, on the shorter arm, the distance 

 of which from D' is so regulated that the weight 

 of the arm D' M is slightly in excess. In the lever 

 there is also a screw, s, the point of which is 

 turned upward and rests against the lower and 

 free end of the zinc bar C C. By means of this 

 screw the position of the lever may be altered so 

 as to raise or lower the pencil attached to its 

 extremity M. 



The operation of this apparatus is easily under- 

 stood. When the temperature rises the zinc bars 

 Lengthen about 4 times as much as the glass 

 tubes, I)' rises while C falls, and the lever then 

 turns around a point situated between C and D' and the pencil M is moved upwards. 

 When the temperature falls the opposite effect is produced. 



tl have been informed that at the Brussels observatory a mercurial thermometer is 

 employed, the horizontal tube of which is balanced on a knife-edge, so that the mer- 

 curial column, in expanding, causes the extremity of the tube to incline more and 

 more, thus allowing the indications of the instrument to be registered as a dial in- 

 strument. 



Fig. I. 



