9) 
NATURE 
[ApriL 18, 1907 
planetary gear drives may be used, and where silent 
running is desired with total enclosure, and a_ right- 
angled transmission is permissible, there is nothing to 
equal worm’ gear, which shows to best advantage for 
reductions of 15 or 20 to 1. 
We have received from Messrs. Wratten and Wain- 
*“ Verichrome ”’ 
plates for photomicrography, together 
wright specimens of their M screens and 
“Allochrome ”’ 
with an explanatory booklet. 
and 
The screens, nine in number, 
consist of gelatin films impregnated with dyes which admit 
the passage of light of certain wave-lengths, the values of 
which are given. We have examined spectroscopically the 
light transmitted by each of them, and find it to be 
correctly stated in the booklet, which also contains a table 
of the absorption bands of the principal staining agents, 
together with the proper screen and plate that should be 
used to photograph a specimen stained with any of the 
named. The booklet contains a concise statement 
of the principles involved, of the method of combining the 
screens, directions for tricolour work, exposure, develop- 
ing, &c. The plates are undoubtedly some of the best 
for photomicrography that have yet been placed on the 
market, and the “ Allochrome ’’ plates will be found very 
useful in ordinary work by those who desire pictures of 
natural objects showing the proper gradations of light and 
shade. A criticism which might be made is that the 
gelatin screens are somewhat delicate, being easily affected 
by damp and heat (it is true they may be obtained 
cemented between two glass plates, but are then much 
more costly). We have no hesitation in saying that 
Messrs. Wratten and Wainwright have made a distinct 
advance, and have brought out their screens and plates on 
lines far more scientific than has hitherto been done. 
stains 
Tue London Geological Field Class has arranged its 
excursions for the study of the London district, under the 
direction of Prof. H. G. Seeley, F.R.S., to commence on 
Saturday, April 27. Mr. J. W. Jarvis, St. Mark’s College, 
Chelsea, is the honorary secretary. 
Tue Halifax Education and Publie Library Committee 
has arranged for the publication of a series of descriptive 
pamphlets on the more important objects in the Bank- 
field Museum under its care. We have received a copy 
of the fourth of the series, sold to the public for one 
penny, which is on ‘‘ Egyptian Tablets,’’ and is written 
by Mr. Thomas Midgley, curator of the Bolton Museums. 
The tablets in the Halifax Museum were brought from 
Thebes to. this country by Mr. Jeremiah Rawson about 
1839. They were built into the wall of one of the rooms 
of the Halifax Literary and Philosophical Society, and 
remained practically forgotten until eight years ago, when 
they were transferred to the Bankfield Museum, walled 
in, and covered with glass. The pamphlet contains the 
result of Mr. Midgtey’s work in deciphering the tablets. 
The inscriptions all consist of prayers to various gods that 
funeral offerings of food, drink, and so on may be given 
to the deceased in an after life. Mr. H. Ling Roth, 
honorary curator of the museum, contributes a preface to 
the pamphlet. 
Mr. Epwarp M. Lanctey, of Bedford, writes announcing 
the discovery of an. interesting contribution to the history 
of English mathematics in the form of a hitherto un- 
published letter by the discoverer of ‘‘ Taylor’s theorem.” 
The letter in question was addressed to the Rev. Mr. New- 
come, fellow of St. John’s College, Cambridge, under 
NO. 1955. VOL 75] 
j light of modern 
date November 24, 1711. In alluding to the appoint- 
ment of Saunderson to the Lucasian chair of mathematies 
at Cambridge, Brook Taylor expresses his opinions on the 
then prevailing spirit of mathematical teaching in the 
following words, which possess considerable interest in the 
thoughts on the subject. The writer 
says :—‘‘ I am very glad Mr. Saunderson has it and hope 
he will fully answer the expectations the Electors have of 
him. He is an extraordinary Algebraist, and I expect 
great Improvements in that Art from his hand; but (if I 
might have my desire) I would rather wish he would apply 
himself to the cultivation of Pure Geometry. That is a 
large subject, worthy of the labours of a Professor, and is 
abundantly more entertaining than the Contemplation of 
mere abstract quantities, which are the proper objects of 
Algebra; but that, truly speaking, is but an introduction 
to Mathematics as Logic is to Philosophy. And it is my 
opinion that the prevailing humour of treating Geometry 
so much in an Algebraical way has prevented many noble 
discoveries that might otherwise have been made by follow- 
ing the methods of the Ancient Geometricians.”’ 
Tue report of the Hampstead Scientific Society for the 
year 1906 shows that the work of the society has con- 
tinued in a uniformly satisfactory manner. The society 
has been added to the list of ‘‘ associated societies ’’ of 
the British Association, and is affiliated to the South- 
Eastern Union of Scientific Societies. The Christmas 
juvenile lectures were successfully repeated, and a nature- 
study course for the benefit of those teaching young children 
was conducted by Mr. W. M. Webb. 
THE general report on the operations of the Survey of 
India during the survey year ending September 30, 1905, 
has now been published. It was during the year with 
which the report deals that the Government of India 
appointed a committee to consider, among other matters, 
the state of the maps in each province and the measures 
required to bring them up to date. This committee has 
since reported that in many parts of India the maps are 
so out of date as to be of little use, and in some cases 
even misleading, owing to changes in roads since they 
were prepared. In order to carry out the recommendations 
of the committee it will be necessary to revise in the field 
practically the whole of the existing 1-inch maps of India, 
and to survey on either the 2-inch or the 1-inch scale the 
whole of the country for which maps on neither of these 
scales have ever yet been prepared. Omitting the 
Baluchistan Agency and the tribal area of the North-West 
Frontier Provinces, it is estimated that an area of 525,800 
square miles of original survey will have to be re-surveyed, 
that a practical re-survey will have to be made of 479,000 
square miles, while the maps of 266,300 square miles may 
be capable of revision in the field. There remains an area 
of 266,300 square miles fer which cadastral maps are or 
will be available from which to prepare topographical maps 
with inconsiderable corrections in the field, and 135,900 
square miles, chiefly in Burma, for which the maps are 
modern, and merely require re-drawing. It is proposed 
that the whole of this work should be carried out within 
twenty-five years, while the survey of Baluchistan, the 
North-West Frontier Province, and the country adjacent 
thereto should be completed within a much shorter period. 
Tue reviewer of the ‘‘ Zoological Record "’ in last weelk’s 
Nature (p. 557) regrets to’ find that in the notice he 
omitted the second n in Tyrrannosaurus and Tyranno- 
Saurus. 
