424 



NATURE 



[Sept. 9. 1875 



and the black types. Pairs belonq; sometimes to one type, very 

 ofien to two different types ; generally the young are completely 

 black or completely white. 



M. Giard gave an account of his researches on some contro- 

 verted points in the embryogeny of theJAscidians, more especially 

 Molgtda socialis, which he has studied in the zoological labora- 

 tory of Wimei^eux. He has been able to supplement and correct 

 in several respects the conclusions of previous observers. M. 

 Giard also, after long research into the embryogeny of animals 

 belonging to the various classes into which Cuvier divided the 

 Articulata and Mollusca, proposed another limitation of these 

 two groups. Another paper by the same was concerned with 

 the embryogeny of the pectinibranchiate Gasteropoda. 



Prof. Sirodot described in detail the results of his researches 

 on Elephants. M. Sirodot remarked that, having had at his 

 disposal a very large number of teeth, he had been able not only 

 to correct the errors committed by Falconnet and De Blainville, 

 but, moreover, to feel confident that the different species of 

 Elephas hitherto described as closely allied to the Mammoth 

 have no value whatever. There are a multitude of inter- 

 mediate forms connecting the Elephas prirtiigeniiis with Elephas 

 indicus. 



M. Lortet, while in Syria, made some investigations into the 

 organisation and reproduction of fibrous sponges. He has been 

 able to prove the presence and to follow the formation of the 

 male and the female egg. Apart from these genital products, he 

 did not meet, in the sponges which he examined, any other 

 cellular element. M. Lortet did not observe, moreover, any 

 canals running into the great canal of the ovule, canals referred 

 to by a large number of zoologists. M. Lortet also described 

 his observations on the very peculiar fauna of the Lake of 

 Tiberias. This fauna appears to indicate a former communica- 

 tion between the waters of the lake and those of the sea. 



Physics. — M. Cornu indicated a very simple process for deter- 

 mining with accuracy the focal distance and the principal points 

 of lenses. 



M. Merget explained the very interesting results of his 

 researches on the thermo-diffusion of porous and humid pulveru- 

 lent bodies. A ihermo-diffuser is generally a porous vessel, 

 filled with an inert powder, in the middle of which is a glass 

 tube or a metallic tube riddled with holes. On heating such an 

 apparatus, after having moistened it, steam is disengaged in 

 abundance through the porous substance, while dry air traverses 

 the apparatus in an inverse direction, and escapes by the tube. 

 If this escape be prevented, there is produced a pressure which 

 reached three atmospheres at a dull red heat. If the pulverulent 

 mass or the porous body ceases to be mo st, no gas escapes. 

 The author did not explain the fact, but he showed that the 

 explanation of it given by M. De la Rive cannot be accepted. 

 M. Merget is convinced that there is here a thermo-dynamic 

 phenomenon. Thermo-diffusion must play an important part 

 in the gaseous exchanges of vegetable life ; the author showed 

 this by taking a leaf of Neluinbium as a thermo-diffuser. 



M. Gripou communicated to the Section and repeated various 

 experiments which he had performed with films of collodion. 

 In receiving upon a Savart polariscope light polarised by a 

 lamina of collodion, we have there systems of fringes, one normal, 

 the other due to phenomena of secondary interference. By 

 illuminating a film of collodion with the light reflected by a 

 second film, we easily obtain fringes of interference, as in the 

 experiment of Brewster. Collodion films are very diather- 

 manous for luminous heat ; they are less so for dark heat. 



M. Mascart showed some very curious experiments on the 

 condensation resulting from the expansion of moist air. If a 

 little water is placed in the bottom of a perfectly clean flask, 

 closed by a glass tube terminated by an indiarubber syphon bag, 

 we have a closed space, which soon becomes saturated with mois- 

 ture. By pressing on the bag the temperature rises, and there 

 can be no condensation. But by allowing the bag to resume, 

 by its elasticity, its original form, the air expands, is con- 

 sequently cooled, and, contrary to what is usually observed, 

 no condensation takes place. To produce the condensation 

 ordinarily observed, it is sufficient to introduce into the flask 

 some unfiltered air, while filtered air produces no effect. In the 

 same way very beautiful clouds are obtained by introducing a 

 little tobacco smoke, or gases resulting from any kind of com- 

 bustion. These experiments may be of some use in explaining 

 the formation of clouds. 



M. Deprez presented an ingenious electric chronograph, 

 intended to estimate by the graphic method intervals of time 

 extremely small, as ihe duratioji of a shock. 



M. Cornu explained his experiments on the rate of light, by 

 the method of M. Fizeau. (See Nature, vol. xi. p. 274). 



Dr. Moreau explained some points in his investigations on the 

 swim-bladder of fishes, and showed particularly that in pro- 

 portion as a fish sinks the effort which it must make diminishes. 



M. Dufet read a paper on his researches into the electric con- 

 ductibility of pyrites. 



In the Section of Geolo!>y xnA Mineralogy, most of the papers 

 referred to local topics. Of those of general interest we men- 

 tion the following : — M.Henry Dufet described his experiments 

 on the thermic conductibility of certain schistose rocks, from 

 which he drew some interesting conclusions regarding the deform- 

 ations of the fossils contained in such rocks. M. Charles Velain 

 read a paper on his exploration of the islands of St. Paul and 

 Amsterdam, while en the expedition for observing the Transit of 

 Venus. M. Lory presented some considerations on the dislo- 

 cation of rocks in mountainous countries. 



Botany. — In this section M. Sirodot gave an account of his 

 researches on the classification and development of Batracho- 

 spermum, and M. de Lanessan spoke on the floral organogeny 

 of Zoster a. 



M. J. Chatin described the results of his histological and 

 histogenic researches on the interior leaf glands and some 

 analogous productions. After having studied the mode of 

 formation of the structure of the^e various organs in many 

 families, he draws the fjllowing conclusions : — i. The interior 

 leaf glands originate always in the mesophyll. 2. These glands 

 are formed by differentiation from a cellule in which mul- 

 tip ication by division is rapidly produced, so that except in 

 some Lnuracex the gland is always formed, in its perfect state, 

 from a cellular mass, more or less considerable. 3. The products 

 of secretion are constantly forming in the cellules proper of the 

 gland. 4. The elements of the latter are re-absorbed from the 

 centre to the circumference, and thus form a reservoir where the 

 product of secretion is amassed. 5. In certain plants, and by an 

 analogous phenomenon, there may be formed in the leaf true 

 secreting cana's. 6. The leaf-glands are almost constantly 

 situated in the vicinity of the fibro-muscular bundles. 7. In 

 many plants there exist at different points of the stalk, of the 

 branches, and of the petioles, certain productions on the whole 

 comparable to the interior leaf-glands. 



M. Merget gave the result of his researches on the interchange 

 of gases between plants and the atmosphere. He concluded with 

 the following statements : — I . The means by which the interchange 

 of gases is effected in plants are the stomataand accidental open- 

 ings ; it is by diffusion in the stomata, and not by dialysis through 

 the cuticle, that exterior gases penetrate into the interior of a 

 plant, and that internal gases escape. 2. The entry of atmo- 

 spheric gases is due to the action of the physical force produced 

 by the phenomena of gaseous thermo-diffusion. M. Merget 

 concluded by some interesting details on the function of chlo- 

 rophyll. 



M. Baillon read a very interesting communication on the 

 Amentacere, 



In the Section of Anthropology, we note the following 

 papers : — Dr. Lagneau read a careful and elaborate memoir on 

 the ethnogeny of the populations of the N. W. of France, in 

 which he reviewed the various peoples which have contributed to 

 the formation of the former and present population of the region 

 comprised between the sea, the Saone, and the Loire. — M. 

 Chauvet read a report relative to the excavations undertaken by 

 the Archaeological Society of Charente, in the tumuli on a woody 

 plateau near a Roman road, and entered into details of a nature 

 to clear up certain controverted points of prehistoric archaeology. 

 From the objects found in these explorations, M. Chauvet 

 develops a doctrine according to which there was no gap 

 between the various civilisations from an industrial point of 

 view. 



As usual, a very large number of papers belong to the Section 

 of Medical Sciences ; some of these are of more than merely 

 technical interest, but our space prevents us from referring to 

 them in detail. A full report of the proceedings will be found 

 in the Revue Scientijique for August 28 and following weeks. 



THE AMERICAN ASSOCIATION FOR THE 

 ADVANCEMENT OF SCIENCE.— DETROIT 

 MEETING 



THE American Association for the Advancement of 

 Science held its twenty-fourth annual meeting 

 at Detroit, Mass., from Aug. 11 to 17 inclusive. Some of 



