524 A UNIVERSAL METEOROGRAPH, 



the index, rubs without sensible friction, tracing a white line upon it. 

 These lines may subsequently be fixed by dipping the paper in gum watei 

 or thin varnish. 



It would be better, instead of the blackened paper, to use a plate 01 

 glass blackened in the same way. When the observations are recoiled, 

 the plate may be laid on a piece of paper impregnated with silver-salt 

 and both exposed to the light ; the lines where the lampblack has been 

 rubbed off will then print black on the paper. If scales, in degrees or 

 hundredths of an inch, as well as time divisions, have been engraved on 

 the plate by means of a diamond, we will readily obtain on the sensitive 

 paper all the data required. The first exposure to light gives, as we 

 have said, the reproduction in black lines of the curves traced by the 

 feather points; then if, leaving the sensitive paper firmly fixed under 

 the glass plate, we clean the latter with a cloth so as to remove all the 

 lampblack, except what is left in the grooves made by the diamond, and 

 the plate be again exposed a short time to the light, the whole surface of 

 the paper will assume a gray tint, on which the curves previously ob- 

 tained will stand out in black, while the diamond rulings will be in white. 

 After being treated with hyposulphite of soda and washed in water this 

 will give a permanent table of observations which may be reproduced 

 by photography if, instead of sensitive paper, we use a collodion film, to 

 be afterwards employed as a negative. 



We will see presently that the direction and velocity of the wind and 

 the amount of rain-fall may be recorded by straight lines, so that these 

 indications may also be made on the blackened glass plate by means of 

 a feather point. 



There is, therefore, no difficulty in fitting up a detached observatory, 

 which may be visited, for example, twice a month, and in which an 

 ordinary clock, running 15 days without being rewound, registers obser- 

 vations which the meteorologist does not care to examine before the ex- 

 piration of that period. The difficulty commences only when the meteor- 

 ologist from his station at the principal observatory wishes to know 

 at each instant the indications of the instruments at the more or less 

 distant observatory, in order to compare the phenomena observed at 

 the two stations. 



II. 



DETACHED OBSERVATORIES TRANSMITTING RECORDS. 



Let us take an aneroid barometer having, as is usually the case, on the 

 glass cover a second index for the purpose of comparing the state of the 

 barometer at any given instant with that of a subsequent time, llemove 

 the glass plate, maintaining the second index, however, in its position 

 above the index of the barometer, and give to the latter a uniform motion 

 of rotation around its axis. In other words, let us imagine an aneroid 

 barometer without glass cover, and opposite to it a clock so placed that 



