APRIL 7; 1904 | 
WIA TORE, 
D9 
paper knife. 
left unread. 
While on the subject of referees, I should like to protest 
against the impatience of many secretaries, who seem to 
expect the poor referee to neglect his university duties at a 
minute’s notice and to give up his whole time to preparing 
a report for return post. 
If Mr. Basset were to start a ‘‘ British Journal of Mathe- 
matics and Physics ’’ without adopting the referee system 
or some equivalent, what would he do when X. Y. Z. sent 
him a paper disproving the existence of gravitation, when 
L. M. N. wrote proving that the ether consisted of jerk- 
backs of energy, or when P. Q. R. called men of science 
fools for not agreeing with his view that the sun’s photo- 
sphere was composed of diatoms of electricity ? 
All the same, a journal of the kind suggested, if published 
of a convenient size, and with the pages cut, would fill a 
distinct want which certainly exists. G. H. Bryan. 
This inevitably means so many more papers 
Euclid’s Definition of a Straight Line. 
I nave long thought that by the words é& tcov, commonly 
translated evenly, Euclid means symmetrically. The 
symmetry can be tested by turning the line over; for in- 
stance, the edge of a flat ruler is straight if, when turned 
over, it coincides with its original position. 
If a long rigid body is rotated, while two points, one in 
each end, retain their places, every line of particles joining 
the two fixed points describes a surface of revolution, which 
is symmetrical (in the sense intended) with respect to the 
two fixed points. The innermost of all such surfaces is of 
vanishing breadth, and is Euclid’s straight line. 
J. D. Everett. 
11 Leopold Road, Ealing, March 29. 
Spawning of the Plaice. 
With reference to the letters of trof. Herdman and Mr. 
W. Wallace as to the commencement of the spawning of 
the plaice this season, it may be stated that in the Moray 
Firth plaice were found spawning in the last week of 
December, and that spawning is not yet completed. The 
time mentioned is rather earlier than usual for this district, 
and it is not unlikely that spawning has been accelerated by 
the mild winter. T. Wemyss Futon. 
Aberdeen, March 29. 
Fossil ‘‘ Rain-drops.” 
TuE preservation of impressions of rain-drops in slabs of 
Triassic marl has always presented some difficulty, since 
mud that was soft enough to receive such impressions would 
seem too soft to retain them. 
I have to-day, at the borders of a flood plain, in a back- 
water of the Dorn Valley, near the Cherwell, seen exactly 
similar impressions in some stiff marly clay from which the 
flood water has lately subsided, where the surface of the 
tongues of clay is covered with the foot-prints of herons, 
rooks and smaller birds, with sun-cracks gradually widen- 
ing until the clay curls into separate flakes, and the 
characteristic “* rain-drop ’’ pittings dispersed over the sur- 
face upon which no rain has fallen since the water subsided. 
This led me to seelx another cause for these peculiar marks, 
and I soon found their origin. The film of mud over sand 
was in some cases still covered with about an inch of quiet | 
water, and the decaying vegetation in the mud had given 
rise to innumerable bubbles that rested unbroken upon the | 
mud bottom, like the bubbles adhering to the sides of a | 
tumbler of soda-water. As the water very slowly leaves 
these bubbles some of them break, and some become coated 
(by surface tension, I suppose) with a thin film of mud which 
strengthens the dome, so that they can become larger, as 
, end of the spectrum. 
they also become flatter, and sink slightly into the tenacious | 
mud, which then contracts slightly away, so that the 
diameter of the circle is enlarged. When at length they 
disappear, they leave circular pits behind them in the half 
dried mud with a slightly raised ring edge, and finally, when 
the mud has completely dried, these shallow rounded pittings 
present exactly the appearance of Triassic ‘* rain-drops ”’ 
amongst the sun-cracks and foot-marks already alluded to. 
I have not seen any such explanation of these “* rain- 
drops,’’ but it seems to remove a difficulty. 
Oxford, March 19. 
NO. 1797, VOL. 69] 
E. C. SPIcer. 
THE USE OF LIGHT AND OTHER RADI- 
ATIONS IN THE TREATMENT OF DISEASE. 
@ Re of the most interesting fields of medical re- 
search at present is the investigation of the 
therapeutic properties of various rays, and although 
much has been accomplished in a few years, there is 
promise of a still greater future for this development 
of the healing art. Any advance in medical science 
is of the greatest moment to the general public, and 
cannot be too widely known, and in this respect this 
branch of therapeutics has had a measure of publicity 
which is probably unique, but which is not altogether 
free from harm. The discussion of purely medical 
details, and the description of ‘‘ cures’ of apparently 
hopeless cases in the columns of the lay Press, have 
unfortunately led to misconception and to terrible dis- 
appointment to many sufferers. 
The fact that certain rays of light possess special 
physiological properties has been long known, and 
valuable papers on the subject were presented to the 
Royal Society as far back as 1872 by Downes and 
Blunt. But the credit of rendering the knowledge 
obtained by these and other observers of practical value 
in the treatment of disease belongs to Finsen, of 
Copenhagen. His first work was to show that the 
chemical rays of light, the violet and ultra-violet rays 
of the solar spectrum, have a deleterious influence 
upon the eruption of small-pox, and this led him to 
introduce the red light treatment for this disease. 
The patient is confined to an apartment from which 
| the chemical rays are excluded by means of red 
curtains. For the treatment to be successful the 
curtains must be thick enough to exclude the chemical 
rays as completely as they are excluded by the photo- 
grapher from his plates and films. In a patient under 
these conditions the ordinary course of the small-pox 
eruption is modified, the fever of the second stage is 
lessened, and the scarring is infinitesimal. It is not 
claimed that the mortality from this terrible disease 
is materially diminished by the light treatment, for in 
a certain proportion of cases there is no hope from the 
first, but in a large majority suffering is diminished, 
convalescence is easier, and disfigurement is slight. 
Finsen’s next work was the development of the light 
treatment for lupus. Lupus vulgaris is a very chronic 
destructive disease of the skin and mucous membranes 
caused by the bacillus of tubercle, the microbe which 
attacks and destroys the lungs in consumption. The 
chemical or actinic rays are here the therapeutic agents 
used. These rays have a definite germicidal power, 
and they are also capable of setting up a peculiar form 
of inflammation. ‘They are the cause of sun-burns and 
of pigmentation of the skin from exposure to the sun’s 
rays. In the treatment of lupus the rays of the sun, 
or, more conveniently in northern climates, those of a 
powerful electric are light, are concentrated by means 
of lenses upon the diseased area. For the lenses rock- 
crystal must be used, because ordinary glass obstructs 
the passage of a considerable proportion of the rays 
in the ultra-violet part of the spectrum. When the 
sun’s rays are used a light filter is employed to cut out 
as.far as possible the heat rays at the red and yellow 
The light filter is a hollow lens 
filled with a solution of methylene blue or an ammoni- 
ated solution of the sulphate of copper. If the electric 
light is used the light filter is now dispensed with, as 
the proportion of heat rays is much less than in the 
rays of the sun. Even with the light filter a certain 
proportion of heat rays pass, and in using either the 
| sun or the arc light it is found necessary to cool the 
| 
surface under treatment. This is effected by placing 
in contact with the area treated an apparatus through 
which a current of cold water is constantly passing, 
