June 29. 1888.J 



SCIENTIFIC NEWS. 



603 



and diffuse at its edges, which can be seen only with 

 small magnifying powers. 



The study of these rings seems to promise certain 

 interesting revelations in celestial mechanics, e.g., 

 the explanation for the anomaly found by M. 

 Baillaud for the mean movement of Tethys, the satellite 

 which revolves on the exterior margin of the densest 

 ring. Another point is the detection of the actual slow 

 transformation of a nebulous ring into a satellite. 



JORDAN'S PHOTOGRAPHIC SUNSHINE 

 RECORDER. 



AT a meeting of the Royal Meteorological Society a 

 paper was read by Mr. Jordan on an improved 

 form of this instrument, by means of which the record is 

 obtained in a straight line at right angles to the hour 

 lines printed on the chart, instead of in two curved lines 



-*.^^ 



Fig. I. 



varying in the amount of their curvature with the 

 seasons of the year, as was the case with the original 

 instrument. The new form of instrument consists of 

 two semi-cylindrical boxes, or dark chambers, into which 

 the sensitised charts are inserted. These are attached to 



whole is attached to a triangular stand, fitted with 

 levelling screws. 



The construction of the instrument will be more clearly 

 understood by reference to the illustrations. Fig. i is a 

 general view of the instrument adjusted at an angle for 

 taking observations in a latitude 51 degs. Fig. 2 is a 

 plan showing the semi-cylindrical chambers AA, the 

 dotted lines indicating the direction of the solar rays as 

 they enter the apertures BB at the different hours of the 

 day. ELF is the triangular plate on which the cylinders 

 are fitted, and which is pivoted on the centres GG. JK 

 is the divided arc. The projecting screens CC are for the 

 purpose of determining accurately the conclusion of the 

 morning and the commencement of the afternoon record, 

 and are so adjusted that the shadows projected from these 

 edges shall fall vertically on the apertures at noon. At 

 the moment of noon both charts receive the rays of sun- 

 shine, but immediately before and after they fall on one 



Fig. 2. 



of them only, so that no more sunlight than is necessarj' for 

 obtaining the record is allowed to enter the dark chamlaers. 

 Some of the advantages gained by this form of the 

 instrument over the previous one will be apparent : i. 

 The trace of sunshine is always recorded in a straight 



Tlfx 



swniiii^i inm,\ 



Fig. 3. Copy of a Chart. 



a flat triangular plate at an angle of 60 degs. to each 

 other, and are capable of adjustment to any angle, accord- 

 ing to the latitude of the station. When the instrument 

 is placed in proper position facing due south, one of the 

 cylinders faces the south-eastern horizon and the other 

 the south-west, the former receiving the direct solar rays 

 from sunrise to noon, the other those from noon to sun- 

 set, in each case the rays entering the chambers through a 

 narrow aperture situated in the centre of the circle, on the 

 inner surface of which is placed the sensitised chart. The 



line. The measurement of it is thereby rendered more 

 simple and accurate. 2. The apertures for the admis- 

 sion of the rays are so placed that each presents a full 

 front to the horizon, thereby giving greater advantage 

 for the recording of early and late sunshine. 3. The 

 fact of the morning and afternoon charts being in separate 

 chambers and independent of each other offers great facili- 

 ties for changing the charts at convenient times of the day ; 

 and although the charts are in two parts, they admit of be- 

 ing joined together as shown in fig. 3, so as to form one con- 



