30 



NATURE 



[May 10, 1883 



On the other hand, where a freshwater stream mingles with the 

 salt water in pools left by the tide, and the endosmotie action of 

 the water set up by its reduced density is greater, the alga; 

 become broader if flat, or of more inflated character if tubular. 

 This is well seen in Dumontia filiformis, Enteromorpha intesti- 

 nalis, and Chondrus crispus. The influence exerted by the 

 character of the surrounding medium and pressure may also 

 be observed in that interesting genus of freshwater plants, 

 Callitriche. E. M. Holmes 



Solar Halo 



I BEG to forward herewith diagram and remarks of solar 

 halo as observed here to-day, thinking it may be of interest, 



being an unusual phenomenon. The cause depends upon 

 many circumstances necessary for such observations, chiefly a 

 calm reflecting surface of water in front, behind, and around 

 the observer, making their appearance local as well as un- 

 frequent. 



The halo marked A, caused by the sun's rays passing through 

 the thin cirri, was reflected froai the surface of the water on the 

 English Channel side of the island, producing the large white 

 halo B, and passing over the san's centre, the non-concentric arcs 

 c being most probably reflected from the harbour side, the 

 bright iridescent arcs at D on the large white halo B being the 

 reflected crossings of the two halos at E. I have fixed the points 

 of the zenith and due south horizon as approximately as possible; 

 the observer facing due south, the iridiscent arc D was nearly 



Solar Halo as observed at Portland, Djrset, April 28, 18 



vertical, and about the same distance from the sun's centre to 

 the estimated centre of large halo B, viz. 12°; the diameter of 

 halo B was a little over double that of A. 



Latitude of Verne 50 32' 86" N. 



Longitude of Verne 2° 23' 40'' \\ . 



Altitude of highest point of Verne 495 feet above sea-level 

 (Ord. B.M.). 



Time (local): first observed at 12.20 p.m.; brighter aspect 

 12.30 p.m.; duration about three-quarters of an hour. Cloud, 

 thin cirri, with cumulo-stratus low in northern horizon. Amount, 

 9. Wind, S. E. Cardwell, 



Late Supervisor Meteorological Department, Bombay 

 Verne Citadel, Portland, Dorset, April 28 



I send inclosed a diagram of a system of solar halos observed 

 here on Saturday last. If one may credit the oldest inhabitant, 

 the phenomenon is very rare in these latitudes ; iu fact the 

 ancient mariners frequenting the New Key End declare they 

 never saw the like in all their wanderings. 



My attention was first called t3 it at 12.25 p.m., when it 

 presented the appearance I have depicted ; but I am told that 

 earlier in the day a white halo was seen south of the sun. The 



smaller circle bad the sun for its centre, round which the sky 

 was of a leaden cast as far as the edge ; the fringed portions 

 represent brilliantly coloured partial halos, or corona?. The 

 larger circle was, as near as I could guess, 40° diam. Its cir- 

 cumference cut the centre of the smaller circle, was brilliantly 

 white, perfectly defined as seen from here, and narrow. I am 

 told that, seen from high ground some four miles from here, it 

 presented the appearance of two horns. The phenomenon 

 lasted after I observed it about an hour, during which time a 

 peculiar haze was drifting over the sky, which, when viewed 

 carefully, seemed to have a hair-like structure, especially when 

 seen parsing the bright edge of the larger halo. I may add 

 that the surface wind was southerly, the drift of the haze S.S.E. : 

 a line joining the centres of the circles would point E.N.E. at 

 about one o'clock. Tho. B. Groves 



Weymouth, April 30 



Mock Moons 



The explanation of the phenomenon observed on the 16th 

 ult., which is given by " Sm." of Rugby, appears to me to be 

 scarcely satisfactory. According to the usual explanation of 

 halos, parhelia, and paraselene, which attributes them to refrac- 





