172 SCIENCE. 
of be the time required by the front of a ray in moy- 
ing from nto ™m, or vice versa. During the first inter- 
val let x and 2’ alone be open. The rays between the 
screens at the conclusion of the first interval are 
shown in the first diagram. During the second in- 
terval let y alone be open, and let the reflector at y’ 
send the ray impinging on it towards z. The situation 
of the rays at the end of the second interval are shown 
in the second diagram. During the third interval let 
x and z alone be open. The rays between the screens 
at the end of this interval are represented in the 
third diagram. During the fourth interval let 7 
alone be open, and let the reflector at y send the ray 
from that point toward 2. The next interval is a 
repetition of the first, and so on. 
It is seen that, in fact, the difference in the direc- 
tions of the two rays arriving at B can be made less 
than any assigned finite angle, however small, by 
sufficiently increasing the distance between the 
screens, or sufficiently decreasing the space between 
the openings, or both. 
It is possible that the above process may, from its 
comparative simplicity, conduce to a clearer under- 
standing of the relations involved, though it seems 
inferior to the one originally proposed in some im- 
portant particulars. H. TT: Eppy: 
University of Cincinnati, Feb. 2, 1884. 
The Greely relief expedition. 
In view of the comment upon the Greely relief ex- 
pedition, it may not, be out of place at this early date 
to call attention to a neglected principle of arctic 
navigation which bears with full force upon the 
navigation of the route in question. ‘To its adoption 
may be traced the success of Nares with the Alert 
and Discovery, and of Nordenskidld with the Vega; 
to its neglect, the wreck of the Jeannette and the Pro- 
teus among a host of others. 
Simply stated, it is, under all circumstances, to 
cling to the coast, and among its islands find protec- 
tion against the floating ice. To coast along the edge 
of the floe, and follow the openings it offers, is a veri- 
table siren. Of course, the principle is not applica- 
ble till after Jones’s Sound is passed; but here the 
course is usually free. 
The Eskimo knew me as 
New Haven, Conn., Feb. 2. 
TILITOIANIAC. 
The red skies. 
I have only time to-day to reply very briefly to your 
editorial inquiry on p. 380, as to previous instances of 
red skies and voleanic eruptions. 
You will find a West India instance in 1831 on 
p. 165 of the Meteorological mayazine tor 1883; but the 
most striking parallel has been pointed out by Pro- 
fessor Karsten of Kiel as occurting in 1783, lasting 
about four months, and spreading over the whole of 
Europe, northern Africa, and eastern Asia. 
Arrangements are being made for the concentration 
of all collectible information upon the subject, and I 
shall be proud to act as the receiver of copies of. any 
notes or records which your readers may intrust to 
me. G. J. Symons, F.R.S. 
62 Camden §q., London, N.W., 
Jan. 25, 1884. 
{We shall publish Professor Karsten’s article next 
week. | 
Aeolian ripple-marks. 
On the evening of June 11, 1883, after a severe 
rain-storm, during which large quantities of soil were 
washed from adjacent fields and deposited along the 
[Von. IIL, No. 
roadside, I noticed near Brodhead, Wis., a peculiar 
phenomenon, which may be worth recording. The — 
mud, deposited only a few hours before, was still — 
very mobile, and, at the point where best seen, cov- 
ered an area a rod or more wide and three or four 
long, presenting a perfectly plane surface. The 
steady force of the strong wind was interrupted by 
occasional gusts of greater violence, each of which 
raised on the plastic mud-surface corrugations, which, 
in every detail that could be caught during their 
momentary existence, resembled ripple-marks formed 
by water, being a beautiful and distinct series of 
parallel ridges slightly concave toward the direction 
of the moulding-force. The outlines of these aeolian 
ripples were no sooner defined than they began to 
dissolve, and a minute or two sufficed to obliterate 
all trace of them. The phenomenon was observed 
several times on the same surface, and also in adja- 
cent localities, where the consistence of the mud. and 
therefore the duration of the ridges, varied slightly. 
The ripples were best defined in the thinnest mud, 
though this was most favorably situated for their 
production; and they disappeared less rapidly where 
formed in the more viscous material. 
This, of course, is not a radically new phenome- 
non, but a rare phase of the familiar action of wind 
on liquid surfaces. R. D. SALISBURY. 
Winchell’s ‘ World-life.’ 
Will you permit me to announce that’a number of 
errata, attributable both to author and proof-reader, 
have found their way into my late work on ‘ World- 
life;’? and I will be glad to mail slips of corrections 
to any who will kindly notify me by simple postal- 
card that they so desire? 
ALEXANDER WINCHELL. 
Ann Arbor, Mich. 
THE LABORATORY IN MODERN 
SCIENCE. 
Tue material circumstances under which 
scientific discovery is prosecuted have been 
completely revolutionized during the last forty 
years. Of the immense changes that have oc- 
curred, the majority have fallen within the last 
fifteen, one might almost say dozen, years. It 
is interesting and profitable to contrast the 
past with the present in this respect. 
Forty years ago there were very few, more 
properly no laboratories which we of to-day 
would consider even tolerable. Now every 
university of importance and high repute, the 
world over, has large suites of rooms for each 
department of science, and often numerous 
great buildings within whose walls thousands 
and thousands of students are daily brought 
face to face with the facts and laws of nature. 
The generation that is now gone pursued its 
scientific studies in incommodious quarters, 
and even those were destined for the use of 
the professors rather than the students. 
a small, dingy, and ill-lighted room is still to 
be seen, where some illustrious savant created 
new knowledge,— a small square chamber, with 
crooked walls, low ceiling, undulating floor, — 
‘? 
we 
——— a areas 
Many 
