530 



A UNIVERSAL METEOROGRAPH, 



ing wire to the positive pole of a battery, the negative pole'of which is 

 connected in the same way with the minute hand, the current will then 

 pass so long as the gold point rests in contact with the divided circle, 

 but when the point meets one of the indexes the current will be inter- 

 rupted for an instant by the interposition of the ebouite tip, but will be 

 restored so soon as the point is freed from that obstacle. 



When the minute hand has traversed the entire circle — that is to say, 

 nfter an hour's time — the current will have been momentarily interrupted 

 (in the example we have chosen) six times. These interruptions may 

 now be made use of at the central observatory, which communicates by 

 means of a telegraph wire with the outlying observatory, to record the 

 indications of the instruments on a cylinder covered with a sheet of pa- 

 per, rotated by clock work once an hour, 

 the rotation of which is therefore isochro- 

 nous with that of the minute hand at the 

 outlying station. 



The isochronism of the two movements 

 is the condition on which the accuracy 

 of the meteorograph depends ; in order 

 to judge if it is fulfilled, little ebonite 

 plates cec are fixed on the divided circle. 

 We will see, later, how these plates give 

 the desired in formation in regard to the 

 working of the clock at the detached ob- 

 servatory. 



On the spindle of the registering cylin- 

 der (Fig. V) is cut a screw-thread which 

 runs in the nut p, so that at each revolu- 

 tion the cylinder descends a little — for 

 example, a millimetre (Jg- inch.) 



Beside the cylinder an electro-magnet, 

 A, is placed, which attracts a piece of 

 soft iron, b b, hinged at d, to which is 

 attached a pencil, steel point, or diamond, 

 pressed against the cylinder by a spring. 

 While the current is closed the pencil is 

 kept away from the cylinder, but at each 

 interruption of the current in the de- 

 tached observatory it is pressed against 

 the surface of the cylinder and makes a 

 dot or a line upon it. When the current 

 is again closed, the pencil is again with- 

 drawn by the action of the magnet. 

 A glance at Fig. V will suffice for the perfect understanding of this 

 ■svsteni. The straight lines o o which Bftrve to regulate the isochronic 



Fig. V. 



