630 
work which are clearly written and well illustrated. A 
little more space might have been given to the construc- 
tion of bell indicators and to the maintenance and pecu- 
liarities of batteries, both of more importance to the 
wireman than the details of the manufacture of electric 
incandescent lamps. Also the distribution of lamps to 
give the best illumination, the use of globes and shades, 
and the ageing of incandescent lamps are all subjects on 
which wiremen would be wise to be informed, which 
are dealt with either inadequately or not at all. There 
is a question we should like to ask: Is Mr. Clinton 
correct in saying that the B.C. holder is known as the 
“bottom contact”? We had always thought that the 
letters stood for “ bayonet cap,” and certainly “ bayonet 
holder” is much the more general phrase. 
Finally, we may add that the book should be useful to 
the wireman entering for the City and Guilds examina- 
tion in this subject; he will find it a valuable travelling 
companion as he proceeds to the examination room. 
M. S. 
The Common Spiders of the United States. By James 
H. Emerton. Pp. xviii + 225. (Boston, U.S.A., and 
London: Ginn and Company, 1902.) Price 6s. 6d. net. 
THE study of spiders is probably less neglected in the 
United States than in Britain, for writers on general 
entomology like Packard and Comstock have included 
them in their works, and there are several valuable 
books on the subject. Still, spiders are less popular 
than butterflies or beetles, and Mr. Emerton has brought 
out the work before us, illustrated with no less than 501 
illustrations in the text, in which he has given a very 
useful account of the commoner American spiders, classed 
under ten families. Mr. Emerton informs us that there 
are at least 300 or 400 species of spiders to be found in 
the neighbourhood of any city in the United States. 
The introductory matter is very good, dealing with 
structure, habits, collecting, &c., and the diagrams on 
p. ix, showing the undersurface of a spider and the front 
of the head, are particularly clear. So many families, 
genera, and occasionally even species of spiders are 
common to the United States and Europe that a student 
beginning to collect British spiders could not do better 
than use this book in conjunction with Miss Staveley’s 
“British Spiders,” before passing on to the more 
elaborate works of Blackwall and Pickard Cambridge. 
Trees in Prose and Poetry. Compiled by Gertrude L. 
Stone and M. Grace Fickett, Instructors in State 
Normal School, Gorham, Maine. Pp. xi+184; illus- 
trated. (Boston, U.S.A., and London: Ginn and 
Company, 1902.) Price 2s. 
THERE are many methods of nature-study in America, 
and in some more attention is given to the zsthetic and 
emotional sides of education than to the scientific. This 
little book is a collection of extracts from good writers 
showing that trees have often been the source of literary 
inspiration. It is good that children should become 
familiar with the best literature their country provides, 
and when at the same time they have their attention 
directed to the study of nature, the lesson becomes of 
increased value. 
Chart of the Metric System. Constructed by Prof. C: 
Bopp. With a pamphlet of ‘“ Notes.” Pp. 15. 
(London: Williams and Norgate.) 
THIS diagram of the metric units of length, area and 
volume is printed on a sheet of paper about 3 feet 6 
inches by 2 feet 6 inches. The various measures are 
shown full size. To be of the greatest use in class teach- 
ing, the chart should be used in conjunction with models, 
and fortunately these are to be obtained. With the aid 
of the “Notes,” teachers should have no difficulty in 
making the idea of the decimal system easy of compre- 
hension to their pupils. 
NO. 1721, VOL. 66] 
NATURE 
[OcTOBER 23, 1902 
LETIERS TOV THE EDITOR: 
[The Editor does not hold himself responsible for opinions ex- 
pressed by hits correspondents. Neither can he undertake 
to return, or to correspond with the writers of, rejected 
manuscripts tntended for this or any other part of NATURE. 
No notice vs taken of anonymous communications. | 
Vortex Spirals. 
Ir appears that a reference to Dr. W. M. Hicks’s memoir on 
the properties of spiral fluid vortices (Phz/. Trans., 1898), 
inserted in the recent reprint of FitzGerald’s Helmholtz lecture 
of January, 1896 (‘‘ Collected Scientific Writings,” p. 353), has 
suggested the misconception that the idea of spiral vortices 
originated with FitzGerald and was subsequently developed 
by Hicks. 
It is beyond doubt, from the context, that FitzGerald derived 
his knowledge of the possible existence and the properties of 
vortex spirals from the detailed discussion of vortex theories of 
matter and their difficulties, contained in Dr. Hicks’s presidential 
address to Section A of the British Association in September, 
1895 ; in this address, and in papers communicated to Section A, 
that striking extension of vortex theory was explained in illus- 
tration of the structure of optically rotational atoms. This is 
the more certain as Dr. Hicks’s observations (/oc. c7z¢.) as to the 
possibility of the mutual absorption of a pair of Hill’s spherical 
vortices (M. J. M. Hill, PAz’. Zrans., 1894) were mentioned 
by FitzGerald in the same context. J. Larmor. 
October 13. 
Bipedal Locomotion in Lizards. 
THE accounts of bipedal locomo tion among lizards contributed 
by Mr. E. A. Green and Miss R. Haig Thomas are of high 
interest. This peculiar method of progression has been recorded 
by me of the Australian lizards Phystgnathus Leseuri and 
Amphibolurus muricatus, in addition to the frilled species 
Chlamydosaurus Kingz, all belonging to the Agamidz. More 
recently I have found by experiment that a member of the 
American greaved lizards, Tupznambis nigropunctatus, possesses 
a like bipedal habit, and have been informed bya correspondent, 
Mr. H. Preston, that the same locomotive peculiarity is com- 
monly manifested by the allied form Amiaeva Surinamensis 
and also by sundry species of the typical iguanas. Another 
correspondent has informed me that that singular iguanoid the 
basalisk is likewise bipedal, not only on terra firma, but that 
it will also run rapidly over the surface of water in an erect 
position. As is the case with the long-toed aquatic birds the 
jacanas, the feet of the running lizard are most probably in this 
case supported in transit by a more or less substantial sub- 
stratum of water plants. 
The bipedal progression attributed to Lacerta viridis and an 
allied form is, as compared with that of the above-named 
species, relatively incomplete; the tail is not raised clear from 
the ground during locomotion, and neither is the erect attitude 
sustained for any duration of time. The conspicuously greater 
length of the hind limbs that characterises all those species of 
which sustained bipedal locomotion has been recorded is a 
prominent feature in many other types which will probably be 
found to possess the same habit. Among these, members 
of the agamoid genera Goniocephalus, Otocryptis, Japalura 
and Calotes!; some of the Anolids, Uraniscodon and others 
among the Iguanidee, and Cnemidophorus belonging to the 
Teiidze, may be indicated as likely to yield affirmative evidence 
in this direction. W. SAVILLE-KENT. 
Milford-on-Sea, October 9. 
Theories of Heredity. 
Is there not room for some provisional hypothesis which shall 
include both Galton’s and Mendel’s ideas, which are not 
necessarily antagonistic, but may turn out to be as simiultane- 
ously true as the laws of Boyle and Charles, so that the final 
results may be of the nature of a product or resultant? I mean 
that instead of drawing a hard-and-fast line between ‘‘ recessive ” 
and ‘‘dominant ”’ characters we may suppose that these differ like 
heat and cold, in degree but not in kind. So that ‘* dominance” 
may be measured on some scale from 0 upwards, the measure of 
dominance being perhaps a function of the number of generations 
for which a character /as been established. 
1 Since writing this letter, a confirmation of my anticipation in the case 
of this genus has been recordedin Nature for October 9 by Mr. N. 
K. 
Annandale.—W. S- 
