90 



NATURE 



SJIay 27, 1880 



closed liy means of strips of fur, and dried interiorly with chloride 

 of calcium, so that in all weathers the machine acts well. 



Herr Zehfuss has lately given (/r/j'i/. Ann., 4) some personal 

 experiences of the phenomenon of "after images of motion" 

 (about which Plateau and Oppel have before written). These 

 after images may be had, e.g., in a train, if one look at a point 

 on the horizon for a little, then turn to look at (say) a horizontal 

 fibre in the wood of the carriage, or close one's eyes. Motions 

 then seem to be still perceived ; in the latter case, e.g., a stream 

 of sparks seems to be moving to the right (or if the point origi- 

 nally looked at have been between the observer and the horizon, 

 there is a stream of sparks above going to the right and one 

 below to the left). Herr Zehfuss offers a physiological explana- 

 tion, in preference to the partly psychical ones proposed by 

 Plateau and Oppel. Each individual nerve rod, he supposes, 

 has special blood-vessels, wliich, when the original image of a 

 moved object goes to the right, directs the course of the blood 

 to that side, just as in ordinary light the decomposed blood is 

 promptly replaced by fresh. By tliis preponderant direction of 

 blood to the right a heaping up occurs in each retinal element on 

 the right, which gives rise to return currents as soon as the outer 

 cause has ceased to act. As the blood flows back there arise, 

 in consequence of the specific excitability of the rods, those 

 spark-streams, which are projected as elementary motions to the 

 right. 



In a recent number of Wicdciiianit s Annahn (3) Herr Schonn 

 describes a method of making visible ultra-violet prismatically 

 decomposed light in such a way that exact measurements can be 

 made. One feature of it is the use of a disk of fine calking 

 paper saturated with sul[)hate of quinine, and contained in a 

 small cell which is brought close before the Eamsden ocular, 

 which can be directed at once on the disk and on a luminous 

 line (its axis is not inclined like that of Soret's, but coincides 

 with the axis of the telescope). The author gives measurements 

 of the ultra-violet spectrum of cadmium, zinc, and thallium. — In 

 the same number Ilerr Glan describes a " spectro-telescope," 

 W'ith which objects can be seen in any homogeneous colour at 

 will. The instrument has various applications, especially in 

 astrophysics. 



In a paper on the thermic theory of the galvanic current 

 {JVicd. Ann., No. 4) Herr Hoorweg lays down the following 

 propositions : — Wherever two conductors come into contact, 

 motion of heat results in development of electricity ; therefore 

 a constant electric difference arises between the two substances. 

 2. If in a closed circuit, the total sum of the differences of po- 

 tential be different from zero, there arises in tliis circuit a con- 

 tinuous electric current. 3. This current exists at the cost of 

 the heat at one part of the point of contact, and has heat-pro- 

 duction in the other for a result. 4. AH voltaic currents are 

 thermo-currents. 5- The chemical action in the battery and the 

 decomposition apparatuses is a result of the galvanic current. 



An interesting series of experiments has been recently made 

 by Dr. Konig on the vibrations of a normal tuning-fork ( {Fic-J. 

 Ann., No. 3). He finds that, practically, at least to 50'= to 60° 

 of heat, the influence of heat on a tuning-fork may be regarded 

 as constant. Thick tuning-forks are more affected by heat than 

 thin ones of the same pitch, indicating (it is remarked) that 

 change of elasticity, and not change of the length of the arms, 

 is the primary cause of the change of pitch. The influence of 

 heat on tuning-forks of different pitch, and of not very different 

 thickness, is proportional to their number of vibrations. Gener- 

 ally the period of vibration of a tuning-fork is increased or 

 diminished g^jVi by a difference of temperature of 1" centigrade. 

 The general change in pitch of the normal fork Utj = 512 

 vibrations per second at 20", through the temperature difference 

 of I" C. is 0*0572 vibrations per second. Dr. Konig has con- 

 structed a fork which, at any temperatm-e, will exactly give 512 

 vibrations. 



Some quotations by Herr Oehler {IViccf. Ann., No. 3) from 

 Jacob Hermann's work, "Phoronomia sive de Viribus," &c., 

 published in 1716, have a curious significance in relation to the 

 history of the mechanical theory of heat. In the twenty-fourth 

 chapter, " De niotu intestino fluidorum," the following para- 

 graph occurs : — " Hoc nomine non intelligitur hoc loco internus 

 molecularum motus fiuidi cujuscunque in suo statu naturali 

 consistentis, sed is particularam motus, qui in fluidis a causis 

 externis et accidentalibus excilari solet, quo calor praesertim est 

 referendus, qui dubio procul ex concitatiore particularum mo'.u 



in corpore calido a causis externis producitur. Utut vero 

 ejusmodi motus intestinus admodum perturbatus sit, nihilo tamer> 

 minus regula physice satis accurata pro ejus mensura media tradi 

 potest. In another place Hermann offers a demonstration of the 

 theorem that "Calor, casteris paribus, est in composita r.itione 

 ex densitate corporis calidi, et duplicata ratione agitationis 

 particularum ejusdem." 



GEOGRAPHICAL NOTES 



Lieut. A. Louis Palander, of the Swedish Royal Navy, 

 was last week elected a Corresponding Member of the French 

 Geographical Society, in acknowledgment of his brilliant services 

 to geography as commander of the l\'ga during the late Arctic 

 Expedition. We understand that the Swedish Royal Academy 

 of Sciences have just caused a handsome bronze medal to be struck 

 in commemoration of the successful accomplishment of this 

 enterprise. This medal shows on one side the heads of Prof. 

 Nordenskjold and Lieut. Palander, and on the other a well- 

 executed representation of the P^cga surrounded by ice. 



At the Anniversai-y Jleeting of the Geographical Society, on 

 Monday next, the Earl of Northbrook will take the chair for the 

 last time, and will deliver an address on recent geographical 

 progress. The formal presentation of the Royal Medals will also 

 take place at this meeting, though neither of the recipients (Lieut. 

 Palander and Mr. Ernest Giles) can be present. Tlie Duke oiF 

 Edinburgh, Honorary President of the Society, will preside at the 

 Anniversary Dinner in the evening, which will be held, as usual, 

 at Willis's Rooms. 



Lord Aeerdare, it is understood, will succeed the Earl of 

 Northbrook as President of the Geographical Society. 



A BEGINNING is about to be made to carry out Lieut. Wey- 

 precht's proposal for a circle of observing stations around the 

 North Polar region. The Danish Government has resolved to 

 establish a station at Upernivik, in West Greenland ; the Russian 

 Government has granted a subsidy for an observatory at the 

 mouth of the Lena, and another on the new Siberian Islands; 

 Count Wilczek is to defray the expenses of a station on Novaya 

 Zemlya under the direction of Lieut. Weyprecht ; the U.S. 

 Signal Service, under General Myer, has received permission to 

 plant an observatory at Point Barrow, in Alaska ; and it is 

 expected that Canada will have a similar establishment on some 

 point of her Arctic coast. At the Hamburg Conference it was 

 announced that Holland would furnish the funds for a station in 

 Spitzbergen ; and it is expected that Norway will have an 

 observing post on the extremity of the Province of Finmark. 

 This is a good beginning, and we hope that some sort of 

 agreement w ill be established to have all the observations made 

 after a uniform method, otherwise their value will be greatly 

 decreased. 



Baron Eggers, of St. Thomas, West Indies, sends us a 

 prospectus of a plan for the scientific' exploration of the West 

 Indies, especially as regards their natural history, his main pur- 

 pose evidently being to make complete collections of plants, 

 insects, and shells. Such collections he offers at certain rates to 

 all who express their wish to become subscribers, the subscrip- 

 tion to be paid on delivery of the collections. Details may be 

 obtained from Baron Eggers or from his ^ent in Europe, Dr. 

 Eug. Warming, Copenhagen. 



M. Paul Soleillet, who was compelled to return to Senegal 

 in his attempt to reach Timbuctoo, is now in Paris, and expresses 

 his determination to embark again in July, to make another 

 attempt. 



A Society of Geography for the north of France has been 

 established at Douai. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE 



Cambridge. — The election to the Professorship of Mineralogy, 

 vacant by the death of Dr. W. H. Miller, F.R.S., will be held 

 in the Senate House on June 12. 



In the fourteenth Annual Report of the Museums and Lecture- 

 Room Syndicate, Lord Rayleigh, the recently-appointed Professor 

 of Experimental Physics, says :— " On visiting the Cavendish 

 Laboratory in December last, after my appomtment to the Pro- 

 fessorship of Experimental Physics, I was at once struck with the 



