Oct. 25, 1877] 



NA TURE 



559 



of 3ge, gave a circumference at one metre from the ground of 

 I '52 metres, another of eleven years growth gave I '42, and 

 another, planted in fresh alluvial soil, nine years of age, gave 

 I '57 metres — about six inches more, Col. Playfair says, than 

 he could embrace with both arms. To the question of 

 the sanitary effects of Eucalyptus a good deal of atten- 

 tion has been directed. An inquiry was instituted by the 

 Society of Physical and Natural Sciences at Algiers under the 

 presidency of Dr. Bertherand, and the result was that from thirty 

 localities reports were received, all of which speak favourably of 

 the Eucalyptus as a fever preventive. On ihe banks of Lake 

 Fetzara, near Bone, 60,000 young trees of Eucalyptus ghlulus 

 were planted in 1S69. At the present time they have attained 

 a height of from 7 to S metres each, and have, it is said produced 

 a very marked effect on the locality. Such was the feverish 

 condition of this district on the annual fall of the water and the 

 denudation of its banks that the director of the Jardin d'Essai, 

 who went to examine the condition of the plants, was imme- 

 diately seized with a violent fever which lasted twenty days. 

 This gentleman, however, now reports that the miasmatic influ- 

 ences which affected him so strongly then have disappeared, and 

 the mosquitoes which rendered the place uninhabitable have dis- 

 appeared with them. At the great iron mines of Mokta et Hadid it 

 was formerly impossible for the workmen to remain there during the 

 summer ; those who attempted to do so died, and the Company 

 was obliged to take the labourers to the mines by train every morn- 

 i ng, and to carry them back to Bone at night, a distance of 33 kilo- 

 metres each way. From 1S6S to 1870 the Company planted more 

 than 100,000 Eucalyptus trees, and now the workmen ate able to 

 live all the year through on the scene of their labour. Consul PUy- 

 fair advances the following reasons as 'accounting for the causes 

 of the improvement in climate from planting Eucalyptus trees : — 

 "In some places," he says," the trees destroyed miasma by 

 utilising the moisture of the soil in which they were planted, 

 and thus draining marshes ; the emanations from their leaves 

 also may have produced a salutary'effect. They contain a large 

 quantity of essential oil very similar to turpentine, which they 

 emit in great quantities, especially when stiired by the wind, 

 and this acts, it is supposed, as a febrifuge. " We are further 

 told that considerable numbers of Eucalyptus have been planted 

 all along the ^railway from Algiers to Oran. Where this line 

 passes through the Metidja the trees have grown most success- 

 fully, but in the Chelif they have proved almost an entire failure. 

 This, however, may have been due to their receiving no attention 

 whatever after being planted. 



We have received reprints of two papers by Dr. C. Le Neve 

 Foster, one "On Some Tin- Lodes in the St. Agnes District," 

 and the other " On a Deposit of Tin at Park of Mines." 



We have received an interesting little publication, by Mr. 

 Edwin Lees, F.L.S., reprinted from the Transactions of the 

 Malvern Naturalists' Field Club, on "The Forest and Chase of 

 Malvern, its Ancient and Present State," with notices and 

 illustrations of the most remarkable old trees remaining within 

 its confines. 



The additions to the Zoological Society's Gardens during the 

 past week include a Bonnet Monkey {A/acacus i-aJiatus) from 

 India, presented by Mr. Richard Turner ; an'Azara's Yox(Caitis 

 azara:), two Brazilian Cariamas (Cariama cristata), a crested 

 Screamer {Chauna chaz'aria) from the Argentine Republic, two 

 Crab-eating Raccoons (Procyon caucrivorus) from South Brazil, 

 a Yarrell's Curassow (Ctojt carunculata), a Sclater's Curassow 

 (Crax sclateri), a Globulose Curassow {Crax globulosa), a 

 Garden's Night Heron (Nycticorax ganlcni) from BrazU, four 

 Silky Cow Birds {Molothyus botiariensis), a Banded Cotinga 

 (Cotinga ciucta), a Yellow-fooled Thrush {Turdus Jlavtpcs) from 

 Bahia, deposited; an Ostrich (St?uthw camelus) from Africa, 

 received in exchange. 



THE LIMITS OF NATURAL KNOWLEDGE^ 



II. 

 TTAVING considered the capacity of the subject and the 

 -^ ^ accissibility of the object, we must now turn our attention 

 to the copula, i.e., the demands which we make of knowledge. 



As all conceptions which we form of nature are exclusively the 

 results of sensual perception, our knowledge cannot go further 

 than to compare the phenomena we have observed, and judge 

 them with reference to one another. If any phenomenon of a 

 special nature occurred only once, if, for instance, we were the 

 only existing organisms our insight would be extremely limited, 

 because all our knowledge of the human organism we have 

 essentially obtained from its connection with all other organic 

 beings. The comparison of many phenomena gives us a unit or 

 a standard by which we can measure and determine each single 

 one. We therefore obtain just as many measures as there are 

 properties in nature which we can perceive by our senses or 

 which can be inferred from sensual perceptions by our judgment. 

 As these measures are deduced from finite facts they have only a 

 relative value, and our knowledge remains finite for the same 

 reason. 



We therefore understand a phenomenon, we know its value 

 with regard to other phenomena if we can measure, count, or 

 ■wei^h it. We have a clear idea of the size of the lowest fungus, 

 of which we must place some 2,000,000 or 3,000,000 individuals 

 side by side to complete the length of a metre, of the size of an 

 elephant, of the earth, of our solar system, the radius of which is 

 somewhere about 3,000,000,000 miles. We have a clear idea of 

 the time in which a ray of light carries to our eye the writing of 

 a book which we read, and which is about the yTri) a irath part 

 of a second — of the life-time of the lowest fungus wliich in a 

 plant-box or in the human body is replaced by a new generation 

 after only twenty minutes — of the life-time of an oak which 

 may be several thousand years, and of the 500,000,000 years 

 which have passed since the generation of organisms upon our 

 earth. 



Natural bodies are composed of parts ; the value of their 

 internal structure, of their organisation, is exactly determined by 

 the quantity, nature, and arrangement of these parts. They 

 therefore give us the measure by which we judge the compound 

 whole, and with which we measure its organisation as it were. 

 The morphological or descriptive natural sciences by these 

 measurements obtain their scientific data. Chemistry, which at 

 the present time is still an eminently morphological science and 

 which investigates the formation of compounds from elementary 

 atoms, and mineralogy, which presupposes the uniform arrange- 

 ment of molecules, have arrived at a state of great perfection. 

 The common measure for organisms is the cell, and further on 

 the organ ; the common measure for the systematic unities of 

 organic nature (for varieties, species, genera) we find in indi- 

 viduals and generations. 



We are enabled not only to compare the different objects and 

 measure them by one another, but in as far as it changes, we may 

 also compare a system, a unit (tinheitliche) group of things of similar 

 nature, with itself and measure it by itself The knowledge of the 

 change is complete if the later stage is proved to be the necessary 

 consequence of the earlier one, or the latter to be the necessary 

 predecessor of the later one, if one can be constructed from the 

 other, if therefore both stages can be brought into the relation of 

 cause and effect to one another. 



In the elementary domains of the material this causal relation 

 is the mechanical necessity, which for two successive stages 

 demands the equal sum of motion in a certain direction (or living 

 force) and of potential energy. Among the sciences which apply 

 here astronomy ranks first ; next in efficiency are several physical 

 sciences, particularly the mechanical theories of heat and optics. 

 Physiology, or the physics of the organic world, tries to pene- 

 trate into a far more difficult and more complicated domain, by 

 following the footmarks of her older sister. 



In the higher domains of the material we cannot for our causal 

 knowledge uphold the demand for this mechanical necessity. 

 Indeed this is perhaps impossible in the case of all structure. 

 ^ Address delivered at th2 Munich meeting of the German Associa- 

 tion, by Prof. C. von Niigch, of iMunich. (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. Tschernialc, of Vienna. At 

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

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

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

 elaborate work.) Continued from p. 535. 



