58 



NEGRETTI AND ZAMBRA, HOLBOEN VIADUCT, E.G., 



Since the indention in 1853 of Mr. CAMPBELL'S instrument for automatically 

 registering the duration of Sunshine, the subject has become of increasing 

 interest, and improved forms of his instrument have been generally adopted at 

 the principal Observatories and Meteorological Stations where the hours of 

 bright Sunshine are regularly observed and registered. These ingenious 

 instruments are perfect recorders of Sunshine so long as the sky is clear, but 

 are too costly to come into general use by the greater number of observers now- 

 interested in the subject. It is to meet this difficulty that the instrument now 

 introduced has been designed. We believe that it meets all the requirements ; 

 it is accurate in its action, of simple construction, and sufficiently cheap to come 

 within the means of all those who are interested in this comparatively new 

 branch of meteorological science. 



Half Size. 



FIG. 68. 



The action of Mr. JORDAN'S Sunshine Recorder differs entirely from that 

 of the instrument above referred to, inasmuch as the results are obtained by 

 means of photography, instead of by the burning power of the concentrated 

 solar rays ; it is, however, only on days when the atmosphere is a little hazy, or 

 the sun slightly obscured by thin, filmy cloud, that there is any important 

 difference in the record of the two instruments ; at such times the photographic 

 registering instrument will probably show an excess of sunshine, as under 

 certain conditions the thin film of cloud or haze interferes more with the action 

 of the heat rays than it does with the actinic rays. 



The new instrument which is figured on the other side consists of a 

 dark cylindrical chamber, on the inner circumference of which is placed a 

 carefully prepared photographic paper. The ray of sunlight being admitted 

 into this chamber through small apertures in the side, is received on the 

 sensitized paper or chart, and travels around it by virtue of the earth's rotation, 

 leaving a distinct trace of chemical action, thereby registering its duration, 

 and the degrees of its intensity, varied by every passing cloud. The cylinder 

 is mounted on a suitable stand, having simple means of adjustment, for the 

 different seasons of the year, and for the use of the instrument in any latitude. 



Price. Sunshine Recorder Fig. 66 330 



Ditto Fig. 67, with rackwork adjustment and 



clamping screws 550 



A Box containing 100 prepared CHARTS, with instructions- 

 Fig. 68 100 



