SCIENCE 
EDITORIAL COMMITTEE: S. NEwcoms, Mathematics; R. 8. WooDWARD, Mechanics; E. C. PICKERING, 
Astronomy; T. C. MENDENHALL, Physics; R. H. THurston, Engineering; IRA REMSEN, Chemistry; 
J. LE ContTE, Geology; W. M. Davis, Physiography; HENRY F. OsBorN, Paleontology ; W. K. 
Brooks, C. HART MERRIAM, Zoology; 8. H. ScupDER, Entomology; C. E. Bressry, N. L. 
BRITTON, Botany; C. S. Minor, Embryology, Histology; H. P. Bowpircu, Physiology; 
J. S. Binuinas, Hygiene ; J. MCKEEN CATTELL, Psychology; 
J. W. POWELL, Anthropology. 
FRIDAY, SEPTEMBER 29, 1899. 
CONTENTS: 
The Perception of Horizontal and of Vertical Lines 
(with Plate IV.) : PRorerssor B. O. PEIRCE.. 425 
The American Association for the Advancement of 
Science :-— 
' The Devonian System in Canada (Il): J. F. 
SWAFTT EVANS Scrioenenceosteccleciaceeacstecedscescincsnnies 430 
Section B.—Physics: PROFESSOR WILLIAM 
EIVAWE TA OG Ke eee ceiscneiomesceeiiesiacssesisasisiciasiiongetacidteecite 438 
Section I.—Social and Economic Science: PRo- 
FESSOR C. M. WOODWARD...........:0ececeeeeeeeeee 442 
The American Mathematical Society: PROFESSOR 
THOMAS F. HOLGATE..............ceceeeeeeeeeees paeoe CY 
The Work of Foreign Museums: F. A. L........... 446 
Robert Wilhelm Bunsen: PROFESSOR JAS. LEWIS 
ETO WAR octane sccrts cache veitticicewe sinivcu ceituaclsesta Sune 447 
Scientific Books :— 
~ The Anatomy of the Frog: PROFESSOR J. S. 
KINGSLEY. Fischer on Protoplasm: Dr. D. 
T. MacDouGAL. Birch’s Practical Physiology, 
Moore’s Elementary Physiology: PROFESSOR 
FREDERIC 8. LEE. Minet’s Analyses Electrolyt- 
iques: PROFESSOR EDGAR F. Smita. Books 
LEO CHOC loa icariad ddaeedadecnad SosasOdOHRE AS BOGE ELE OoU EE Lena 451 
Scientific Journals and Articles .........c0sssceesereenees 454 
Societies and Academies :— 
The Washington Botanical Club: DR. CHARLES 
WWOUISHROLTAR Ds. c..e-cedesseeeescoosceessebecoentadiets 455 
Discussion and Correspondence :— 
On the Definition of Geological Terranes : 
CHARLES R. KEYES........... 2... 6. 456 
Zoological Notes: F. A. Li ..sseeeeeeeeee ... 458 
Recent Zoo—paleontology: H. F. O.. «- 458 
International Congress of Physics.......01.c0.c0seeeeneee 459 
The Chemical Composition of American Food Ma- 
PUNCETILOIS tonacnsaseceasnenseswiae sac senen eae eaeeee sete Aes aae 
Scientific Notes and News............. 
University and Educational News 
MSS. intended for publication and books, etc., intended 
for review should be sent to the responsible editor, Profes- 
sor J. McKeen Cattell, Garrison-on-Hudson, N. Y, 
THE PERCEPTION OF HORIZONTAL AND OF 
VERTICAL LINES. 
ALMost every person is occasionally 
called on to decide ‘by the eye’ whether 
some straight line is horizontal or some 
other line vertical. It usually happens, as, 
for instance, when one has to set a picture 
straight on the wall of a room, that the 
judgment is helped by the presence, in the 
neighborhood, of other lines, known to be 
nearly horizontal or vertical, but some- 
times all standards are lacking and then the 
decision is a little more difficult to make, 
In order to find out whether such train- 
ing as a student of physics gets from sev- 
eral years of laboratory work is likely to 
improve his judgment in such matters as 
these, and whether astigmatism affects the 
results materially, I have experimented 
in the Jefferson Physical Laboratory upon 
forty persons who kindly consented to make © 
observations for me. 
We used two very simple pieces of appara- 
tus. One of these is a fixed horizontal tele- 
scope, the eye piece of which can turn freely 
in its tube. The eye piece carries a single 
cross hair within, and a large sheet brass dise 
coaxial with the telescope without. This 
disc serves as an eye screen, and carries, on 
the side away from the observer, a divided 
circle which has a fixed reading microscope. 
The observer, sitting in a chair before the 
instrument, with eyes screened from a view 
of extraneous objects, turns the dise while 
