Ocl. 18, 1877] 



NATURE 



531 



K. R. S. Messrs. Blackie will publish a new edition of Thompson's 

 " Gardener's Assistant, Practical and Scientific," revised and 

 xtended by' Thomas Moore, F.L.S., Curator of the Chelsea, 

 Botanic Gardens, &c., assisted by several eminent practical gar- 

 deners ; also " Upper Egypt, its People and its Products," a 

 descriptive account of the manners, customs, superstitions, and 

 occupations of the people of the Nile Valley, the Desert, and 

 the Red Sea Coast, with sketches of the natural history and 

 eology, by C. B. Klunzinger, JI.D., formerly Egyptian Sanitary- 

 Physician at Koseir on the Red Sea. Mr. Jlaclehose, of Glasgow, 

 announces: "Outlines of Physiology," by Prof. McKendrick ; 

 Messrs. Collins: "Building Construction," by R. Scott Brown ; 

 "Machine Construction," by E. Tomkins ; and "Mineralogy," 

 by J. II. Colhns, in their Advanced School Series. 



In a paper in the Jciirnal de Physique, on the spectrum of the 

 electiic spark, by M. Cazin, the author concludes that the 

 electric spark in a gas contains incandescent gas particles, which 

 give a bright line spectrum, and solid and liquid particles which 

 produce the contin^ious spectrum, the former coming from the 

 gaseous medium and the electrodes, the others from the electrodes 

 and the sides near the spark. If the pressure increases, the 

 solid or liquid particles become more abundant, and their con- 

 tinuous spectrum predominates; at last this makes it impossible 

 to distinguish the bright gas lines, or, in other ^^'ords, the latter, 

 while the pressure increases, seems to dilate, and eventually flow 

 together into one continuous spectrum. By making photographs 

 of the spectra M. Cazin found his views confirmed. Of the 

 nitrogen spectrum at ordinary pressure he photographed si.\ty- 

 two lines, using nine cells in the battery giving the spark. 



Herr J. Stei'AN has lately communicated the results of some 

 interesting researches to the Vienna Academy of Sciences, 

 relaiing to the heat-conducting power of several substances. 

 The conducting power of copper being taken as unity, he found 

 that of iron to be 0"i7, ice o'oo57, gUss O'ooi6, water O'ooi5, 

 hydrogen O'ooo39, hard india-rubber o '00026, and air o '00005 5. 



In a recent communication to the Vienna Academy M. 

 Ciamician discusses the spectra of chemical elements and their 

 compounds. He finds, in agreement with Lockyer, that the 

 compound spectra, as well as those of the first order of the 

 elements, consist exclusively of bands ; and further, that band- 

 spectra belong to molecules and molecular groups, line-spectra 

 to free atom.'. From a comparison of the spectra of thirty-one 

 elements he draws these conclusions : I. The spectral lines of 

 chemically-allied elements correspond to each other either 

 individually or group-wise, so that each natural group of elements 

 has its own spectrum, which, in the individual members of the 

 group, is different only in that the homologous lines are displaced 

 towards the one or the other end of the spectrum, i.e., increase 

 or decrease in wave-length, and that certain lines or line-groups 

 disappear, 2. Tlie increase or decrease of wavelengths of 

 homologous lines in chemically-allied elements depends on the 

 intensity of their chemical vis viva, a greater wave-length cor- 

 responding to a greater chemical vis viva of the particular 

 element. 



Although for years there has been no scarcity in France 

 through drought, still the want of irrigation is much/elt almost 

 every summer in the departments of the Mediterranean region. 

 The French Government is about to take measures which might 

 serve as a hint to the Indian Government. A project is being 

 considered for taking advantage of the waters of the Rhone to 

 irrigate systematically that large and already fruitful country. 

 It is impossible to foresee what wonderful changes may result 

 from sue h a scheme, which it is contenoplated to bring into 

 speedy execution. 



The Annual Report of the Queensland Philosophical Society, 

 1877, just received, is a satisfactory one. It contains the address 



of the president. Sir James Cockle, on some of the aspects of 

 the evolution theory. 



The second volume, for 1S77, of Dr. Emilio Huelin's 

 " Cronicon cientifico popular," has just been published at 

 Madrid. In a recent'number we gave a short notice of the first 

 volume. The second volume is in every respect equal to the 

 first. 



The additions to the Zoological Society's Gardens during the 

 past week include two Bonnet Monkeys (Macaciis radiatus) from 

 India, presented by Mr. T. Golding and Miss Ward ; a Layard's 

 Flying Squirrel (Sciiiroptcrus layardi) from Ceylon, presented by 

 Sir Charles Peter Layard ; a Brown Coati (Nasua 7iasica) from 

 South America, presented by Dr. G. P. Best ; a River Jack 

 Yi^ex(Vi/!eiai-hinoceros)hoTaVieit Africa, presented by Mr. 

 I. J. Kendall ; two Red Kangaroos (Macroptis rufus) from 

 Australia, four Chinese Turtle Doves (Turtur chiiiensis) from 

 Java, deposited; a large-billed Crow {Corviis culminatiis) from 

 India, purchased ; a Vulpine Phal anger (Phaloiigista vul/ina), 

 born in the Gardens. 



THE LIMITS OF NATURAL KNOWLEDGE^ 



"TPHE subject of my address was excellently treated at the 

 ■*■ Leipzig meeting in 1S72, by Prof. Du Bois Reymond. If 

 I take up the same matter again, I do so because I would con- 

 sider it from a somewhat different and more universal point of 

 view. 



I shall also depart from the form and language in which the 

 subject has hitherto been frequently treated. In its generality 

 the theme easily induces the speaker to make excursions into the 

 philosophical domain and to adopt the corresponding manner of 

 expressing himself. I shall use words only of the simplest and 

 clearest description, and I shall not suppose my heaiers possessed 

 of anything but a knowledge of the most elementary phenomena 

 in the various domains of nature. In general matters expression 

 is all the simpler and the more intelligible the closer our ideas 

 approach clearness, and, at the same time, truth. I think it 

 advisable, before entering upon the subject itself, to mention 

 shortly the different ways in which the question of the limits of 

 natural knowledge is generally conceived and answered by 

 naturalists. 



Amongst the so-called practical scientific men (Praktiker) the 

 view is widely spread that a certain and lasting knowledge and 

 understanding of natural phenomena is, on the whole, impos- 

 sible. They know that hitherto their systems and opinions have 

 not been permanent, and think that scientific theories generally 

 are only attempts to approach the inaccessible reality, attempts 

 which change their tenor and expression with the views of the 

 time. This is evidently not a view based on principles, but only 

 despair caused by failure, the necessary consequence of wrong 

 method and of scientific incapacity. 



The practical scientific man relies upon his experience, as he 

 says. This, however, is gained in the following manner : — Each 

 natural phenomenon is accompanied by different and often 

 numerous causes and other circumstances. It is the task of the 

 investigator to find out what are the effects of each one of these 

 causes and circumstances ; and this task cannot, in most cases, 

 be accomplished by mere observation. The practical man then 

 selects some cause or circumstance which happens to appear 

 conspicuous to him, and in this he finds the fundamental cause 

 of the phenomenon. This he calls his experience. We there- 

 fore understand how these practical men may hold different 

 opinions upon the same phenomenon, why their views bear the 

 stamp of the scientific epoch, and wliy in course of time they 

 change. We also understand why the theories based on so-called 

 experience are most fertile in those domains where phenomena 

 are most complicated, as in organic morphology, in physiology, 

 and pathology. 



' Address defivered .it iht Munich meeting of the German Associa- 

 tion, by Prof. C. von Niigcli, of Munich. (The author, in a note to the 

 German original, remarks that this lecture had to replace another in the 

 programme, which had been promised by Prof. Tschermak, of Vienna. At 

 the eleventh hour Prof. Tschermak announced his inability to attend the 

 Munich meeting, and ihe author was requested by the secretaries to fill the 

 gap thus occasioned. The address therefore, the author slates, beats the 

 stamp of its hasty origin, as it was written during a journey in the Alps, 

 when there was neither sufficient leisure nor opportunity for careful and 

 ehiborate work.) 



