to somewhat scanty reports, this colored snow fell at least from Dubuque, Iowa, to Chelsea, Vt., in an east-west direction, and from Madison, Wis., to Newberry, Mich., in a north-south direction. It covered an area of at least 100,000 square miles, and probably much more. The total quantity of dust is estimated to have been at least a million tons, and may have greatly exceeded this, perhaps even amounting to hundreds of millions of tons. A study of the character of the dust and of the attendant meteorological conditions led to the belief that the dust was blown all the way from arid regions in the far south-western United States, and was therefore transported a thousand miles or more.-English Mechanic and World of Science, No. 2806.

GRAVITATION.-In the "E.M." of the 20th and 27th of March, 1903, I gave a set of numerical illustrations of the force of attraction between certain chosen bodies, and among them was the following: (1) two equal spheres of water (that is, of a material of density equal to unity), each with a radius of about 241 cm., attract with a force just equal to the weight of 1 gramme.

It may be of interest to add for comparison two other cases : −(2) In order that a single sphere of water should attract a mass of 1 gramme, placed on its surface, with a force equal to the weight of a gramme, the radius of the sphere must have the enormous value of 3,517,732,000 cm., a length 5,527 times that of the earth's radius, and 14,611,810 times that of the radius of either sphere in (1).

(3) If we take a single sphere of 241 cm. radius, it will attract a mass of 1 gramme on its surface with a force of the weight of 1 gramme divided by 14,611,810, an extremely small force. The point of special interest is in the contrast between (1) and (2). It requires a sphere of water, with a radius more than 51⁄2 times that of the earth, to attract a mass of 1 gramme on its surface with a force equal to that with which two equal spheres of water in contact attract each other, the radius of either being less than 8 ft.-CHAS. T. WHITMELL, F. R.A.S., Journal and Transactions Leeds Astronomical Society, No. 25.

J. R. C.

NOTES AND QUERIES

Communications are Invited, Especially from Amateurs. The Editor will try to Secure Answers to Queries.

A NEW TYPE OF NEBULAR SPECTRUM

By degrees we are learning various facts which ultimately will enable us to formulate a consistent theory of the evolution of the stars. One such new discovery was made in the investigation into Hubble's Variable Nebula carried out at the Lowell Observatory and described in Bulletin No. 81 of that institution. This nebula is officially designated N.G.C. 2261, and in the catalogue is described as "cometic", having a nucleus (known as the variable star R Monocerotis) from which streams off the cometshaped nebulosity. The star is at the apex of the nebulous body and is all but separated from it. Unfortunately the nucleus is very faint, being of magnitude 12, and so to obtain a photographi of its spectrum is a long and tedious task.

Quite recently Hubble showed that the nebula was distinctly variable and it was felt that it should prove an interesting object for the spectrograph. Dr. Slipher has made two spectrograms, the second with an exposure of 37 hours, and on examination the spectrum showed a remarkable resemblance to those of Nova Geminorum No. 2 and Nova Aurigae at some of their early stages of development.

The establishment of the fact that this remarkable nebula is of the nature of a nova does not clear up the mystery, but it is very suggestive. By a study of the variations in the form and brightness of the nebula, and at the same time of the changes in its spectrum, we may hope to obtain suggestions as to the nature of

novae. Another nebula, N.G.C. 6729, has been extensively studied. by Knox-Shaw, in Egypt, and Lampland at Flagstaff, and a spectrogram was attempted by Slipher with an exposure of 20 hours. The plate is very weak, but the indications are that this nebula is similar to Hubble's. Though these objects are faint, they come about every year and thus give opportunities for study, while the novae have to be taken when they happen to appear.

COMMERCE AND RESEARCH

For the last three or four years there has been much discussion regarding the place of scientific research in the manufactures of a country, and it certainly has been demonstrated that science can lend great assistance in advancing the production of a nation. In the United States the Bureau of Standards at Washington has carried on some very important investigations into fundamental scientific matters, as well as many with a direct bearing upon trade, while a number of large manufacturing companies have instituted research laboratories of their own. It has been proposed to establish in Canada an institution combining in some degree both the purely scientific and the practical sides of research. The recent meeting of the American Physical Society at Baltimore illustrated the activity of these research institutions. Out of 23 papers on the program, 7 were from workers in commercial laboratories, 6 from the Bureau of Standards and 3 from the Weather Bureau. The remaining 5 came from university laboratories. Of course, this small number for the universities does not fairly represent their scientific activities, as most of the workers were giving their best efforts to the war service of the Government; but the program does show that scientific research has taken root in the manufacturing life of the United States.

A YOUNG MOON SEEN AT 11 P.M.

The attack at midnight on Zeebrugge by the Vindictive and her associated craft was one of the greatest episodes in the war

and, indeed, one of the finest achievements in the annals of the British Navy. It is therefore with some hesitation that I refer to a description of the action written by Lt.-Commander E. Hilton. Young, who was second in command on the Vindictive, which was published in The Cornhill Magazine. In his very interesting account he says:

The picture becomes sharp again at 11 o'clock at night on April 22.... The night was overcast; but there was some star-shine, and also, I think, a low young moon behind the clouds. Altogether there was a faint glimmer of light on the sea, and large objects could be seen dimly some 'five hundred yards away.

Now, I fear a "low young moon" would have set long before 11 p.m.; also I doubt if there was much starshine with an overcast sky. Further, the Nautical Almanac must assert its dignity. and it says that on April 22, 1918, at 11 p.m., the moon was almost 12 days old, that is, well on to full; and at that hour it would be near the meridian and about 40 degrees above the horizon. It no doubt supplied the "faint glimmer of light", which, however, was enough to guide the heroic company in their daring and brilliant. exploit. Captain Carpenter has enumerated so many impossible things which were actually done on that historic night that, if the Almanac had not interposed its record, I would have felt inclined to believe that the venturesome men had been able to keep the "young moon" above the horizon until after 11 o'clock.

66

THE PUBLISHER OF THE BINARY STARS."

In the review of this work in the December number the publisher's name was not given, as it does not appear on the title page. I am asked to state that the publisher is Douglas C. McMurtrie, 2929 Broadway, New York City.

C. A. C.