30 
a very few stones, which had been reddened and crackled by 
fire. No trace of burnt wood, ashes, or bone could be seen. 
It was remarkable that nearly all the stones found were flakes, as 
very few unworked pieces of flint could be lighted on. The 
flakes from the huts differ in condition materially from the flakes 
in the fields below, as all the flakes in the fields are marked with 
dark ferruginous strains, whilst those from the hut-floors are 
perfectly unstained, no iron haying ever reached them. 
In the immediate neighbourhood I have at different times 
found a large number of scapers, a lance-head, a few arrow- 
heads, and a few rudely-chipped celts, some broken. One small 
chipped celt has incurved sides, indicating, as Mr. John Evans 
has pointed out in his work on stone implements, that this 
particular form was possibly an imitation in flint of an early, 
flat bronze celt, 
It is always well to examine the earth brought out of holes by 
rabbits, moles, foxes, rats, and other animals, in places where 
prehistoric relics exist on pasture-land. I have secured a con- 
siderable number of my antiquities from such places. 
Last year I told a young niece of mine to keep a watch on 
such places at the spot where the five large tumuli are placed on 
Dunstable Downs, and where I had on previous occasions 
found flint flakes in the heaps made by moles, &c. It was not 
long before my niece lighted on two pieces belonging to the 
back part of a human skull. They had been scratched out of 
the base of the northernmost tumulus by some animal. Fortu- 
nately the two pieces fitted together ; they are evidently of great 
antiquity, and probably represent part of the person who was 
buried in the tumulus, quite possibly one of the old chippers of 
Neolithic implements. WORTHINGTON G, SMITH 
A Lady Curator 
In Nature for November 27, 1884 (p. 90) you acknowledge 
the receipt of the ‘‘Catalogue of the Natural History Collec- 
tions of the Albany Museum, Grahamstown, Cape of Good 
Hope,” and allude to the ‘‘zealous curator.” Are you aware 
that that individual is a young and accomplished lady? Here 
is another path opened for our daughters and ‘‘ sweet girl gradu- 
ates” to fame and fortune. Those who, like myself, have the 
pleasure and privilege of knowing and corresponding with Miss 
Glanville can appreciate the ardour and zeal with which she is 
following up her chosen vocetion. May every success attend 
her. E. L. LAyARD 
British Consulate, Noumea, February 25 
Hoar Frost 
A COMMUNICATION in NATURE of January 8 (p. 216), in 
regard to frost-formations, leads me to send a word from Maine. 
T have seen frost-work so like the description there given, that 
it would answer very well for an account of frosts in this climate. 
These frost-formations occur when the wind is chilly and blow- 
ing steadily, without the compass veering, for hours. I have 
compared these deposits to the most delicate designs of Oriental 
lace-work. At one time I witnessed an accretion on a wall, 
where the feathery forms were from two to four inches in length, 
with the points towards the wind. I think this is because each 
added particle adhered to the very tip of the previous one. Cer- 
tainly no pen-description can do justice to the delicate beauty 
when the sun suddenly broke through the clouds and shone upon 
this forest of frost-ferns. CAROLINE W. D. Rich 
Auburn, Me., April 
Rainbow Phenomenon 
ON Saturday night, about six o’cl>ck, I observed, at Old 
Trafford, on the west side of Manchester, a rainbow with accom- 
panying phenomena, which I had never observed before. 
Several very heavy showers had occurred during the day. ‘The 
wind was within a point or two of west. At the hour above 
named a cloud was passing over, very dense and uniform in 
colour, and with that dark leaden hue so general in thunder- 
storms. There was, however, no thunder or lightning. Rain 
fell in torrents. As the cloud, which was of large area, passed 
off, the sun shone brightly in the north-west, and a magnificent 
rainbow painted itself on the dense black screen afforded by the 
cloud. ‘The rainbow was double, the prismatic colours, of 
course, occurring in reverse order in the outer bow. The most 
remarkable feature of the display was the sharp contrast in the 
NATURE [May 14, 1885. 
shadow of the cloud, evidently caused by the rainbow. Between 
the two bows it was of the densest leaden hue. Inside the inner 
bow it was exceedingly light coloured, with the faintest suggestion 
of luminosity. Outside the outer bow it was of an intermediate 
grey. The uniform mass of cloud was marked off by the two 
bows with geometrical accuracy into three regions, each perfectly 
homogeneous in itself, but distinctly contrasted with the two 
other tints. The effect was weird and startling, and was ob- 
served and commented upon by several spectators in whose 
company I was. There was another feature connected with the 
inner bow which I have never observed before. The green and 
violet colours were repeated inside the bow. Probably the 
whole tract from green to violet inclusive was repeated, but I 
could only make out those two colours distinctly. 
Have these peculiarities, either or both, been observed before, 
and, if so, how are they accounted for ? CHARLES CROFT 
Prestwich, near Manchester, May 11 
FIVE MATHEMATICAL RARITIES 
A BRIEF reference to some recent reprints, &c., 
by Dr. Bierens de Haan, of Leyden, may not 
be unacceptable, though, unfortunately, ignorance of the 
language in which four of them are written prevents our 
giving more than the barest description of them. 
The “Stelkonstige Reeckening van den Regenboog,” or 
Algebraical Calculation of the Rainbow, is a rare tract, 
by no less distinguished an author than B.de Spinoza. It 
was for a long time supposed to be lost, if not burned ; it is 
here printed in exact facsimile from a copy published at 
the Hague in 1687. Bound up with it is another rarity, 
similarly printed, entitled “ Reeckening van Kanssen,” or 
Caiculation of Chances. No reference to this is made by 
Todhunter. There is a slight probability of this tract 
having proceeded from the same hand, as Dr. De Haan 
cites a reference to the forty-third letter in the collected 
works of Spinoza. 
The third reprint is of a very rare book by A. Girard: 
“Invention nouvelle en l’Algébre, tant pour la solution 
des equations, que pour recognoistre le nombre des solu- 
tions qu’elles recoivent, avec plusieurs choses qui sont 
neécessaires a la perfection de ceste divine science” 
(Amsterdam, 1629). M. Marie writes: “ Cet ouvrage est 
surtout remarquable par les idées justes que l’auteur émet 
au sujet des racines négatives des équations et de leur 
usage en géométrie.” 
The last two tracts have not been before printed: they 
are both the work of Simon Stevin, and are entitled “ Van 
de Spiegeling der Singkonst” (ze. Miroir de Art du 
Chant), and “Vande Molens.” There is a full account 
prefixed to the former of these works, and we learn that 
the latter contains “le calcul de 19 moulins a vent, 
suivant la méthode usitée et suivant une nouvelle méthode 
de Simon Stevin luirméme, qui consiste 4 indiquer les 
roues, les dents et les pignons, afin de satisfaire 4 quel- 
ques conditions données.” 
Thanks are due to Dr. de Haan for the great care with 
which he has brought out these facsimiles, and we think 
he will certainly reap the reward he seeks. We quote 
his words in the last of these volumes: “J’ose espérer 
que la réproduction de ces ouvrages d’un homme si 
renommé pourra intéresser ceux qui s’occupent de 
Vhistoire des sciences.” 
ON CERTAIN SPECTRAL IMAGES PRODUCED 
BY A ROTATING VACUUM-TUGE 
HE beautiful effects produced by the rotation of a 
vacuum-tuhe when illuminated by a series of elec- 
trical discharges from an induction-coil are well known. 
The tube is generally attached to a horizontal axis, which 
is turned rapidly by means of a multiplying wheel; the | 
images due to successive discharges which, if the tube 
were at rest, would be superposed, are thus caused to 
occupy different parts of the retina, and if the discharges 
