480 
WAT RE 
[Marcu 24, 1904 
twenty lengths, printed in successive columns, and 
occupies four pages of the book. This comparatively 
great length enables three significant figures to be read 
off directly from the scale divisions and subdivisions, 
while a fourth figure can be estimated. The author 
claims that computations can be made with a degree 
of accuracy equal to that obtained by the use of four- 
figure log tables, and with less trouble. We suspect, 
however, that few would be found who would allow 
this claim, or be willing to give up their tables for the 
author’s plan. The title of the book is somewhat mis- 
leading ; instead of a ‘‘ substitute for the slide rule,’ 
the proper description would be, a substitute for tables 
of logarithms; the ‘‘ calculating scale’’ is only an 
equivalent for the slide rule in the sense that a log 
table may be so regarded. We fail to see any useful 
purpose that this scale is likely to serve. 
Practical Orthochromatic Photography. 
Bookshelf, No. 14. By Arthur Payne, F.C.S. 
Photography 
Pp. 
178. (London: Iliffe and Sons, Ltd., 1903.) Price 
Is. net. 
In these pages the author gives us an excellent 
account of the fundamental principles governing this 
branch of photography. Although he does not pretend 
to exhaust the subject, yet the reader will find that 
enough of the theory has been dealt with to enable 
him to obtain a good ground-work of the scientific 
principles for his own practical use. The ten chapters 
into which the books is divided treat of the advantages 
of this kind of photography, light, the use of the 
spectroscope, visual and photographic brightness, light 
filters, their use and effects, and other important 
subheads. 
Not only is the letterpress clear, but the numerous 
illustrations are well chosen, and add to the utility of 
the volume. Those about to take up this branch of 
photography, and others who are practising it, should 
find this book a good guide. 
Tombs of the Third Egyptian Dynasty at Reqadqnah 
and Bét Khalldf. Report of Excavations at 
Reqdgqnah, 1901-2. By John Garstang, B.A., B.Litt. 
Pp. 7o+xxxiii plates. (Westminster: Archibald 
Constable and Co., Ltd., 1904.) Price 21s. net. 
AFTER an introductory chapter describing the site of 
the excavations and the nature of the results, Mr. 
Garstang deals with the continuity of early history and 
the place of the third Egyptian dynasty in ancient 
history. Three chapters are then devoted to stairway 
tombs, to their construction, special features, and 
objects from them, respectively. -The evolution of 
stairway tombs is discussed in a later chapter. Other 
sections of the volume are devoted to the necropolis, 
burial customs, burials under pottery vessels, objects 
from the smaller tombs, and the archeology of the 
third dynasty. There are thirty-three full-page plates 
containing a large number of good illustrations. 
Worked Problems in Higher Arithmetic. By W. P. 
Workman, M.A., B.Sc., and R. H. Chope, B.A. 
Pp. viit+144. (London: W. B. Clive, 1904.) 
rice: 2s. 
Tuis useful little book consists of two sections; in the 
first many of the difficult problems in the author’s 
“Tutorial Arithmetic’? are fully solved, while the 
second part, which will appeal more to teachers, com- 
prises solutions of all the problems of Section xi. of 
the same work. The bool should prove of value to 
the private student particularly, who is, we notice, 
warned that ‘‘but little benefit will accrue to him 
unless he makes it a regular practice to attempt to | 
solve the questions for himself before reading the 
solutions here given.’’ 
NO. 1795, VOL. 69] 
LEGER S KORTE Spit OR. 
(The Editor does not hold himself responsible for opinions 
expressed by his correspondents. Neither can he undertake 
to return, or to correspond with the writers of, rejected 
manuscripts intended for this or any other part of NATURE. 
No notice is taken of anonymous communications.] 
Blondlot’s 7-Rays. 
For the past few months I have endeavoured to repeat 
some of Blondlot’s measurements with n-rays, taking every 
precaution and following out closely the methods and 
adjustments described by Blondlot in his numerous papers 
which have appeared during the past year in the Comptes 
vendus of the Paris Academy of Sciences. 
A Nernst lamp consuming 176 watts was used, which is 
described by Blondlot as emitting the rays most copiously. 
A variety of screens of phosphorescent calcium sulphide, 
some brilliantly phosphorescent, others very feebly so, were 
employed for the detection of the rays. The experiments 
were carried out in an absolutely dark room to which the- 
eye had become accustomed by a wait of fifteen or twenty 
minutes, the only light visible being the phosphorescent 
glow of the screen. Lead screens, thickness inch and 
1/16 inch, were used to intercept the rays, and occasionally 
a quartz lens was used to focus them on the screen. 
But in no case could any certain difference in the 
brilliancy of the screen be shown to be due to the presence 
of the n-rays, although the experiments were repeated many 
times and under varied conditions. The only observed 
differences in brightness could be assigned to four known 
causes. If initially the sulphide was fairly bright, after a 
while it appeared less so, owing to the natural decay of the- 
phosphorescence. If the phosphorescence was very feeble 
it appeared more brilliant by indirect than by direct vision, 
this being a well known phenomenon in physiological. 
optics, which has been admirably discussed in the paper by 
O. Lummer, of which a translation appeared in NaTuRE- 
of February 18 (p. 378). 
The third effect was the increase of brightness due to the- 
increasing sensitiveness of the eye during the first few 
minutes spent in a dark room, and the fourth is mentioned 
below. Several competent observers in England and 
Germany have likewise obtained negative results in look— 
ing for what Blondlot describes as being so simple, and it 
seems advisable to direct attention in the columns of NATURE: 
to certain experimental precautions not sufficiently observed,. 
perhaps, by Blondlot in the course of his work. 
A slight rise in temperature increases the brilliancy of 
the screen. Using a screen which showed no appreciable 
brightening under the influence of the n-rays from a Nernst 
lamp, it was found that by heating it gently, perhaps 10 
or 15 degrees centigrade, without using n-rays at all, the 
brightness increases very perceptibly, possibly 50 or 100 per 
cent. as nearly as could be estimated by simple obsery— 
ation; so that efforts to detect n-rays may be partially 
vitiated by the presence of heat effects, from the body of 
the observer, &c., unless special precautions are taken to 
show that this is negligible. Mr. S. G. Brown has brought 
this point forward very clearly in a recent letter to NATURE 
(January 28). 
On reading a recent striking paper by Blondlot on the 
index of refraction and wave-length of n-rays (Comptes 
vendus, January 18), one cannot, considering the experi-- 
mental conditions, fail to be impressed by the extraordinary 
experimental skill required to carry out what Blondlot 
describes. 
In measuring the index of refraction, a comparatively 
wide slit (5 mm.) was used, placed 14 cm. from the filament 
of a Nernst lamp. After traversing the slit, the rays passed 
through an aluminium prism, and were dispersed, each: 
homogeneous pencil spreading out into a_ constantly 
broadening beam. Now in measuring the angles of devi-- 
ation there would be two difficulties to be overcome. The 
beams become so broad, being 1 em. wide at a distance of 
14 cm. from the slit, that the intensity is greatly weakened. 
Furthermore, it may be shown, by using Blondlot’s actual 
values for the indices of refraction, and calculating back- 
wards, so as to get the angles of deviation, by the well 
known formula for Descartes’s method, that among the 
total number there are at least three consecutive beams 
