;8o 



NA TURE 



[February 19, 1903 



unconnected with the nest-cavity, but traversing the fortress 

 from external runs, through which earth has been carried 

 to heap over the nest. Fig. 2 shows a fortress of the most 

 complicated type. 



Except when in marshy soil, nearly every fortress has the 

 aforesaid bolt-run, which leads upwards from the bottom of 

 the nest, and thus outwards, without connection with the 

 other tunnels. More rarely a down-shaft, which may be 

 nearly a yard in length, descends obliquely from the nest. 

 The use of these down-shafts is not apparent. Presumably 

 it is in them that the collections of paralysed worms, sup- 

 posed to be stored up by the mole as food, have been found. 

 Such collections of worms are, however, regarded by the 

 author as accidental. 



The nest-cavity, which is about the size of a large cottage- 

 loaf, and worn smooth by friction, contains a ball of grass 

 or leaves, or a mixture of both, by which it is completely 

 filled. In the case of the English species, at any rate, no 

 fur from the mole's body is used in lining the nest. 

 Apparently a nest is never used for more than one season, 

 but two or even three nests, generally one above the other, 

 may be found in the same fortress, of which the newest is 

 alone in use. In all cases it appears that the female makes 

 a fortress and nest of her own in which to breed, this being 

 usually less complex than that of her partner, and without 

 a bolt-run. Whether previous to the breeding-time the 

 female inhabits the same fortress as the male is doubtful, 

 and it is not improbable that moles are polyandrous. 



It is now demonstrated that the female produces only a 

 single litter annually. The young are usually born between 

 the middle of April and the latter part of June, after a gesta- 

 tion of four weeks ; the number in a litter varies from two to 

 six, three or four being usual. The number of teats in the 

 female is eight, and not, as usually stated, six. R. L. 



THE VISIBILITY OF ULTRA-MICROSCOPIC 

 PARTICLES} 



T N the course of an optical investigation of various shades 

 of ruby glass, Messrs. Siedentopf and Zsigmondy de- 

 vised a method of observing small particles of gold which 

 closely approach molecular dimensions, and thus extending 

 our range of molecular vision very considerably. 



The ruby glasses, examined by the best ordinary micro- 

 scopes, appeared perfectly homogeneous. But the authors 

 reasoned that if the gold particles embedded in the glass 

 were at such distances apart that a microscope could resolve 

 them, they could be made visible even though their size 

 should be a small fraction of the wave-length of visible 

 light. The only condition was that the product of the 

 specific intensity into the surface of the luminous particles 

 and the square of the sine of the effective angle of illumin- 

 ation should be greater than the inferior limit of the sensi- 

 tiveness of the human eye. The problem is thus reduced 

 to that of the visibility of a fixed star. What is seen is, 

 of course, a diffraction disc, and that is all we can hope to 

 see, but the authors indicate a means of determining the 

 true size and weight of the particles seen. 



It is essential that all disturbing side-lights should be 

 avoided. The authors threw a beam of sunlight through a 

 condenser on a slit 0.05 to 0.5 mm. wide, and an image of 

 the slit was produced in the field of vision by a telescope lens 

 and a collimator with a reduction of 36 diameters. The 

 diffraction discs seen in the ruby glass had an average 

 apparent diameter of 1 mm., while their real diameter, 

 calculated from the quantity of gold present and the number 

 of particles counted in unit volume, was 0.02 /j.. on the 

 average. This gives a magnification of 50,000 diameters. 

 The utmost limit to which the magnification can be pushed 

 by this method is about 150,000 diameters, or 6 nfi. The 

 average diameter of a molecule being 0.6 m*., it cannot be 

 seen, even as a diffraction disc, unless its specific luminosity 

 were ten times that of the solar molecules, or the sensitive- 

 ness of the eye were greatly increased. The cumulative 

 effeGts used in photography may be resorted to, but the 

 authors do not mention that possibility. 



rract of a paper by H. Siedentopf and R. Zsigmondy (Annalen dcr 

 physik) No. 1, 1903, pp. 1-39). 



NO. J 738, VOL. 67] 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Oxford. — A meeting of tbe teachers of natural science 

 was held in the examination schools last Saturday to hear 

 the views of a deputation of the Association of Public School 

 Science Masters on the subject of entrance scholarship ex- 

 aminations. It was agreed that two principal subjects 

 should be offered in scholarship examinations, and a sug- 

 gestion was made that the subjects should.be selected from 

 physics, chemistry, botany, zoology and geology. The 

 meeting was divided in opinion as to whether botany and 

 zoology should form one group or two. With regard to the 

 recommendation of the deputation that candidates not offer- 

 ing chemistry and physics should be given an elementary 

 paper in these subjects, the meeting was unanimous as to 

 the desirability of this course, and further suggested the 

 addition for those candidates of a practical examination in 

 elementary chemistry and physics, which should not be con- 

 fined to qualitative analysis. 



Cambridge. — At a conference held on February 7 between 

 representatives of the Association of Public School Science 

 Masters and the college tutors in natural science, the follow- 

 ing recommendations in regard to the college examinations 

 for entrance scholarships and exhibitions were provisionally 

 agreed to : — (1) That the science part of the examination 

 should consist of: (1) Papers and practical work in not 

 more than six subjects, namely, (1) physics, (2) chemistry, 

 (3) §r e °l°&y. (4) ,ne natural history of plants, (5) zoology, 

 (6) the elements of botany and zoology, it being understood 

 that no candidate may take the subject (6) if he take either 

 of the subjects (4) or (5). Of these six subjects candidates 

 must offer not more than two. (2) Candidates who take 

 subjects (3), (4), (5) or (6) should be required to take an 

 elementary paper in physics and chemistry. (3) Candidates 

 who take subject (1) should be required to take an elemen- 

 tary paper in mathematics. 



The vacancy at Caius College, caused by the death of Dr. 

 X. M, Ferrers, F.R.S., has been filled by the election of 

 the Rev. E. S. Roberts, senior tutor to the mastership. 



The Gilbey lecturer in agriculture will give this term 

 a course of lectures on small holdings and allotments in the 

 Chemical Theatre, on Fridays, at 5. 



A report of the Committee of Privy Council in favour 

 of the petitions of the Liverpool University College and 

 Owens College, Manchester, for charters of incorporation 

 as independent universities, was submitted to the King in 

 Council on Moncjay and approved by him. The decision 

 will be received with pleasure by all who are interested in 

 the development of higher education in this country. It is 

 essential that we should have more universities if we are 

 to march with the times. Regional universities are not 

 known in any civilised country, and only end in examin- 

 ations and the destruction of real teaching and research. 

 In the report published in Tuesday's Times, the committee 

 expresses the opinion that as the step involves issues 

 of great moment, and as the effect of the multiplication of 

 universities ought not to be lost sight of, the authorities of 

 the Yorkshire College at Leeds should have the opportunity 

 of submitting a draft charter incorporating a University in 

 Yorkshire before the draft charters sought are finally 

 settled, and that the institutions concerned should be invited 

 to consider in greater detail not only the points on which 

 joint action is desirable, but also the methods by which it 

 can best be secured. The committee also considers that 

 special rights of inspection should be reserved to the King 

 as Visitor, and that careful provision should be made in the 

 charters to secure an effective voice to external and in- 

 dependent examiners in all examinations for degrees. 



Dr. D. J. Cunningham, F.R.S., professor of anatomy in 

 Dublin University, has been unanimously elected to succeed 

 Sir William Turner in the chair of anatomy at Edinburgh. 



Reuter reports that it has been decided to create a chair 

 of commercial science, with a special faculty, in the Uni- 

 versity of Zurich, which is the first on the continent to 

 establish such a chair. 



