55§ 



NATURE 



[April 16, 1903 



wood in an early stage of dry rot, while others depict 

 the spores of the fungus. The life-history of Merulius 

 forms the subject of the third chapter, in the course of 

 which it is shown that moisture aids in its development 

 rind spread. The mode in which it affects wood, and 

 the manner of its propagation, are discussed in sub- 

 sequent chapters, after which the best methods of pre- 

 vention are taken into consideration. A second and 

 much shorter section of the work is devoted to the 

 nature and ravages of Polyporus vaporarius and other 

 wood-destroying funguses. R- L. 



How to Work Arithmetic. Parts i. and ii. By 

 Leonard Norman. Second Edition. Pp. xvi + 77 

 in each part. (Rugby : G. E. Over, 1902.) Price 

 is. 6d. net each. 

 These small volumes contain the same series of 136 

 " model problems worked in full by elementary, and 

 advanced methods " respectively. In part ii., the 

 shorter method of long division is adopted, which 

 makes it preferable to part L, even for beginners; and 

 questions which are solved by the " unitary method " 

 in part i. are solved by " proportion " in part ii. The 

 problems are, many of them, of a somewhat old-fash- 

 ioned and useless character, and while the range is 

 fairly comprehensive, the omission of examples of 

 methods of approximation seems remarkable. There 

 is a misprint in the recurring decimals which are 

 "worth knowing"; the terms "odd" and "even " 

 instead of " alternate " in the test of divisibility by 11 

 are apt to be misleading. Every pupil with a good 

 teacher ought to make a collection like this for himself, 

 but the books should prove useful to self-taught 

 students. 



Untersuchungen iiber den Lichtwechsel Algols. Bv 

 Ant. Pannekoek. Pp. xxiv + 236. (Levden : L. van 

 Nifterik, igo2.) 



In this volume the author has collected and discussed 

 the chief observations of Algol that have been made 

 since the publication of John Goodricke's results in 

 ■783. 



The observations of Plassman, Argelander, Heis, 

 Miiller, Wilsing, the author and others are included, 

 and the various methods of obtaining and interpreting 

 thi results are analysed and compared. 



The construction of comparison-star light scales, 

 photometric measurements, the magnitudes at. and 

 the duration of, the maxima and minima, the construc- 

 tion of the light curves and their asymmetry, are 

 amongst the other subjects which are discussed in 

 detail. 



There are two appendices, the first of which deals 

 with the corrections which have to be applied to these 

 observations, whilst the second gives the details of the 

 observations of Plassman, Pannekoek, Argelander and 

 Heis respectively, in tabular form. W. E. R. 



My Nature Notebook. By E. Kay Robinson. Pp. ii 

 + 211. (London: Isbister and Co., Ltd., nn>v) 

 Price 2X. 6d. 



During 1902, Mr. Robinson contributed weekly a series 

 of interesting " nature notes " to the Dai7v Graphic, 

 and the fifty-two instalments are here re-published in 

 book form. Under each week are to be found five or 

 six short paragraphs, describing in a chatty way certain 

 aspects of nature noticeable at that period of the year. 

 To the intelligent person living in the country, such 

 a book as this should prove of great use, for under 

 the author's guidance there will be no difficulty in 

 knowing what and how to observe, and quite a short 

 experience of such personal observation will develop a 

 love for plants and animals of many kinds. 



NO. 1746, VOL. 67] 



LETTERS TO THE EDITOR. 



Thr Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Wither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any oilier part of NATURE. 

 No notice is taken of anonymous communications.] 



Can Dogs Reason ? 



The answer to the question, " Can an animal reason? 

 depends upon the sense in which the word " reason " is 

 used. If dog-stories are to be accepted as evidence, the 

 question must be answered in the affirmative, even though 

 the most liberal, and human, significance be attached to the 

 word. It is, however, of great importance that data should 

 be obtained under conditions which can be rigidly con- 

 trolled, in order that the credibility of anecdotes may be 

 tested by the results of observations which can be easily 

 repeated. Already excellent work has been done in this 

 field by Lloyd Morgan, Thorndike, Small, Mills, Hob- 

 house, and others, but the science of animal psychology is 

 still in its infancy. 



That an animal can compare a sensation newly received 

 with memories of sensations, and form a perceptual judg- 

 ment, which leads to action suitably adapted to its circum- 

 stances, no one doubts ; but this is hardly reasoning in the 

 usually accepted meaning of the term. We may, for the 

 sake of simplicity, term the forming of a perceptual judg- 

 ment putting one and one together. But can an animal 

 compare an inference with an inference? Is it capable of 

 what we term the syllogism, when speaking of human 

 thought? Can it " put two and two together" within the 



common meaning of this phrase? 1 am, of course, con- 

 scious of the absurdity of applying the term syllogism tc 

 the wordless thought of an animal, and also of the fact 

 that a perceptual judgment may be expressed in syllogistic 

 form, but my meaning will, I think, make itself sufficiently 

 clear in the description of the following experiment : — 



An exceptionally intelligent fox terrier was taught to open 

 a box by lifting a wooden latch with its nose. Some care 

 was spent upon the design of this box (Fig. 1). The latch 

 was in the first instance long, and therefore easily lifted. 

 Behind the door was placed a spiral spring, which could be 

 twisted until it exerted any degree of pressure which seemed 

 desirable. As the dog learnt to lift the latch, the length of 

 the latch was curtailed. At the same time the spring was 

 tightened until it pressed against the door with a degree 

 of force which made the latch so stiff that the dog could not 

 lift it without deliberate effort. There was no risk of its 

 being opened by a chance movement. The dog was re- 

 warded with food for performing the trick, which soon be- 

 came so familiar as to be a game. As often as the door 

 was closed the dog opened it. If he found the box on the 

 floor he invariably opened it without waiting for any sign. 



