SCIENCE 
EDITORIAL CoMMITTEE: S. NEwcoms, Mathematics; R. S. WooDWARD, Mechanics; E. C. PICKERING), 
Astronomy; T. C. MENDENHALL, Physics; R. H. THURSTON, Engineering; IRA REMSEN, Chemistry; 
J. LE Conte, Geology; W. M. Davis, Physiography; HENRY F. OsBoRN, Paleontology ; W. K. 
Brooks, C. HART MERRIAM, Zoology; S. H. ScuDDER, Entomology; C. E. Brssry, N. L. 
BRITTON, Botany; C. S. Minot, Embryology, Histology; H. P. BowpitcH, Physiology; 
J. S. Britines, Hygiene; J. MCKEEN CATTELL, Psychology; DANIEL G. BRIN- 
TON, J. W. POWELL, Anthropology. 
Fripay, Juty 7, 1899. 
CONTENTS: 
Knowledge and Practice: PROFESSOR CHARLES 
SEDGWICK MUNOD)..-. 0 -cecceoce-ecasacssesnnsenesesses 1 
Lord Kelvin’s Address on the Age of the Earth as 
an Abode fitted for Life (I1.): PROFESSOR T. C. 
CHAMBER UNM eran torn see sncstinsncteeciccacscosesssinece 11 
A Dangerous European Scale Insect not hitherto re- 
ported, but already well established in this Country : 
IDR Cielo CART AUD a scores snactionecescesescec sens 18 
Cross-education: WALTER W. DAVIS..............- 20 
Scientific Books :— 
Ratzel’s History of Mankind: PROFESSOR OTIS 
T. Mason. Canada Experimental Farms Re- 
port: WALTER H. Evans. Books Received... 21 
Scientific Journals and Articles. ...........0ccecceeeeeees 23 
Societies and Academies :— 
The Geological Society of Washington: Dr. W. 
F. Morseuu. Texas Academy of Science: PRo- 
FESSOR WILLIAM L. BRAY. Torrey Botanical 
(GUMS 13s (Sb LB Xeno}. sscocsasuoesooccoootudscoacsone 24 
Botanical Notes :— 
The Popularization of Botany ; Report of the Mis- 
sourt Botanical Garden ; Atlas of Officinal Plants : 
PROFESSOR CHARLES E. BESSEY.............000055 27 
Measurements of Asylum Children: F. A. L........ 29 
Scientific Notes and News........-..sssececssecscnsecccssace 29 
University and Educationul News 
MSS. intended for publication and books, etc., intended 
for review should be sent to the responsible editor, Profes- 
aor J. McKeen Cattell, Gai fison-on-Hudson N. Y. 
KNOWLEDGE AND PRACTICE.* 
Tuer honor of delivering the address upon 
this occasion is great ; the responsibility of 
appearing as the successor of the distin- 
guished men who have addressed you in 
* Yale University Medical Commencement Address, 
June 29, 1899. 
previous years is also great, yet, as I thank 
you for your generous welcome, I feel, most 
of all, the pleasure of being the guest of 
Yale. To a Harvard man an honor be- 
stowed by Yale has a special and very 
pleasant value. 
Yale and Harvard have been working 
together for two centuries ; their aims have 
always been similar; their developments 
have been parallel, and they have long 
sought one another for those friendly con- 
tests, intellectual and athletic, which yearly 
renew the close bonds between the two uni- 
versities. I hope that their experience has 
been mutually helpful, for I am sure at least 
that Harvard has often learned from Yale, 
and they both have the same problems to 
solve if necessary. 
Just at present there is a whole series of 
urgent problems in medical education before 
both institutions, and I shall, with your per- 
mission, try now to contribute to the dis- 
cussion of some of those problems. You, 
who are upon the eve of graduation, know 
that you have received a far better prepa- 
ration for the practice of medicine than was 
possible for any one to obtain a generation 
ago. You owe this advantage to the con- 
stant recognition of the possibility of im- 
provement in medical education, and you 
should carry forth the feeling that it is now 
your duty to promote further progress in 
the organization and methods of medical 
schools. It is, therefore, eminently fitting 
