SCIENTIFIC SUMMARY. 
333 
that the waves are in every way analogous to those already studied by 
Professor Guthrie in artificial troughs, and follow the laws which he has 
deduced from his experiments. Most of the experiments in Switzerland 
were made on the Lake of Geneva, but that of Neuchatel was found to be 
best fitted for the study of the subject, possessing, as it does, an extremely 
regular geometric form. The apparatus he employed was very sensitive to 
the motion of the water, being capable of registering the waves caused by a 
steam-boat half an hour after it had passed, and five minutes before its 
arrival ; and was so constructed as to eliminate the effect of common waves, 
and to register the motion, side by side, with a record of the state of the 
barometer, on paper kept in continuous motion. While he found the dura- 
tion of waves to be ten minutes at Morges it was seventy minutes at Geneva, 
and this is explained by the narrowness of the neck of the lake at the latter 
place. This period he proved to be independent of the amplitude, and to be 
least in the shortest lakes. For shallow lakes the period is lengthened 5 and 
his observations show that the period is a function of the length and depth, 
and that longitudinal and transverse waves may co-exist, just as Professor 
Guthrie has shown to be the case in troughs. 
Imitation Snoiu Crystals. — M. Dogiel, of St. Petersburg, selects a sub- 
stance which crystallizes like snow, in a great variety of forms of the 
hexagonal system. And this substance is iodoform. To show the multi- 
plicity of forms, M. Dogiel dissolves iodoform in boiling (90 per cent.) 
alcohol, and lets the solution cool in water of different temperatures. He 
gets mostly tabular crystals, when a solution containing 15 to 30 per cent, 
of iodoform is kept ten minutes in water of about 14° to 15° C. ; whereas 
star-shaped and often very complicated crystals are had at temperatures of 
26° to 37°. Some other modifications of the result are described by M. 
Dogiel, in a paper recently published, and he also gives drawings of the 
crystals he obtained. 
A Remarkable Atmospheric Phenomenon at Ceylon . — The Dev. P. Abbay 
sent a communication on this subject to the Physical Society, May 27. In 
speaking of several of these phenomena he says that the most striking is 
witnessed from the summit of Adam’s Peak, which is a mountain rising 
extremely abruptly from the low country to an elevation of 7,200 feet above 
the sea. The phenomenon referred to is seen at sunrise, and consists ap- 
parently of an elongated shadow of the mountain, projecting westward to a 
distance of about 70 miles. As the sun rises higher it rapidly approaches 
the mountain, and appears at the same time to rise above the observer in the 
form of a gigantic pyramid of shadow. Distant objects may be seen through 
it, so that it is not really a shadow on the land, but a veil of darkness be- 
tween the peak and the low country. It continues to rapidly approach and 
rise until it seems to fall back upon the observer, like a ladder which has 
been reared beyond the vertical, and the next instant it is gone. Mr. Abbay 
suggests the following explanation of the phenomenon : — The average tem- 
perature at night in the low country during the dry season is between 70° 
and 80° F., and that at the summit of the peak is 30° or 40° F. consequently, 
the low strata of air are much the less dense, and an almost horizontal ray 
of light passing over the summit must be refracted upwards and suffer total 
internal reflection, as in an ordinary mirage. On this supposition the veil 
