828 



SCIENCE. 



[N. S. Vol. XXI. No. 543. 



is tlierefoi-e less ground for change of gen- 

 erally accepted opinions than the sviggestion 

 of the need of revision might for the moment 

 indicate. 



The second consideration concerns the proc- 

 esses of combined induction and deduction by 

 which the complete or logical method of scien- 

 tific investigation is constituted. In view of 

 the possible change of interpretation now open 

 for truncated uplands according to Passarge's 

 law, it might be said by one who prefers 

 to work on more purely inductive lines : " Be- 

 hold, here is another case in which deduction 

 has led the investigator astray! He thought 

 that he cotild deduce the sole conditions under 

 which truncated uplands could be formed, and 

 that these conditions necessitated uplift after 

 degradation ; now he finds a new series of con- 

 ditions under which such uplands may be 

 formed and all. his previous conclusions are 

 uncertain. Let us, therefore, beware of de- 

 ductive or imaginative methods, and hold fast 

 to the safer methods of observation and induc- 

 tion." In reply to such a warning, one might 

 say — besides pointing out that all problems 

 which deal with unseen processes necessarily 

 involve deduction and that the deductive side 

 of the work should be conscious and systematic 

 — that the fault in the method by which trun- 

 cated uplands have heretofore been discussed 

 lies not in the too free use of deductive 

 methods, but in their too limited use. The mis- 

 take lies in our not having years ago set forth, 

 by purely deductive methods, just such an 

 analysis of the geographical cycle in an arid 

 climate as has now been provoked by the dis- 

 covery of rock-floored desert plains. Such an 

 analysis does not involve any new or diiEcult 

 I)roblems; it might have been successfully at- 

 tempted long ago; the difficulty that stood in 

 the way lay not in the problem itself, but 

 rather in the habit among physical geographers 

 of trusting too largely to observational 

 methods and of neglecting the aid that de- 

 ductive methods furnish. The lesson of the 

 problem is, therefore, that deduction should 

 be pushed forward more energetically and sys- 

 tematically than ever; always checking its re- 

 sults as far as possible by confronting them 

 with the api)ropriate facts of observation, but 



never halting in the reasonable extension of 

 deductive conclusions because the correspond- 

 ing facts of observation have not been de- 

 tected ; never lessening the activity with which 

 exploration and observation are pursued, but 

 always using the spur of deduction along the 

 paths suggested by ' multiple working hypoth- 

 eses.' The problem of the erosion of moun- 

 tain valleys of Alpine glaciers teaches the 

 same lesson: if physiographers had, thirty 

 years ago, been well practised in deductive 

 methods, they might have easily extended 

 Playfair's law regarding the accordant junc- 

 tion of branch and trunk streams from the 

 case of stream surfaces to the contrasted case 

 of stream beds, and from the case of water 

 streams to the analogous case of ice streams ; 

 thus they might have predicted that, if Alpine 

 glaciers were etfective eroding agents, glaciated 

 mountain valleys ought to show discordant or 

 hanging side valleys; and in going to the 

 mountains they would have found the predic- 

 tion correct, and the basis of the prediction — 

 that glaciers are effective eroding agents — - 

 would have thus been verified. So with the 

 geographical cycle in an arid climate: there 

 is nothing difficult in the series of deductions 

 that lead to the expectation of rock-floored 

 desert plains, independent of baselevel, as the 

 product of arid erosion; the only obstacle to 

 the development of these deductions has been 

 the habit of not making them. This is a 

 habit that should be broken. 



W. M. Davis. 



NOMENCLATORIAL TYPE SPECIMENS OF PLANT 

 SPECIES. 



The recent ' Code of Botanical Nomencla- 

 ture ' now usually known as the Philadelphia 

 Code, states as the fourth fundamental prin- 

 ciple, ' The application of a name is deter- 

 mined by reference to its nomenclatorial type.' 

 This means that a specific (or subspecific) 

 name stands or falls according to the disposi- 

 tion of the type specimen. It is not proposed 

 here to discuss the advantages or disadvan- 

 tages of tliis method of determining the appli- 

 cation of names, although to the writer this 

 method seems much more likely to secure 

 ' stability, uniformity and convenience in the 



