482 



NATURE 



{March 27, 1879 



how little probability there is of migratory birds flying at great 

 elevations, and that even in low latitudes, the temperature at 

 altitudes exceeding four and a half miles would be prohibitory 

 to the existence of the majority of migrants : — 



Altitude. Temp. F. Temp. F. 



O 



5.000 



IO,CXX3 



15,000 



20,000 



25,000 



30,000 



Calculations by Mr. Glaisher's rule for approximate temperature 

 (decrease of i° F. for every 300 feet elevation) give less startling 

 results than the above, but even then, with the thermometer 

 marking 80° at sea level, we find that a temperature of 40° of 

 frost must exist at five miles in height. 



The advocates of the "sight theory" have rather more in 

 their favour than Prof. Newton has conceded to them. It is 

 not necessary that birds should fly at such heights as to literally 

 view the land they guide their course to or by. The " loom " 

 of land, so well known to .^ailors, is visible when the land itself 

 is below the horizon ; and I do not think we are entitled to say 

 that birds would not, equally with mariners, notice the indica- 

 tion. Then again the action of one flock of birds when in 

 sight of land, might guide other more distant flocks, and the.«e 

 might influence birds still further offl We know how the circling 

 downward swoop of a vulture on some discovered carrion will 

 draw to the feast vultures from all parts of the sky. We know 

 the power of our own vision, certainly inferior to that of many 

 birds ; and it is therefore well within the bounds of possibility 

 that migrating birds, watchful because weary and hungry, may 

 see and be influenced by the movements of flocks of their com- 

 panions thirty to forty miles distant. A few flocks might thus 

 bridge a wide expanse of barren ocean. 



It is not necessary, however, to insist that sight alone is the 

 guiding faculty in migration. The majority of, if not all, 

 animals possess that marvellous *' sense of direction " that has 

 become so blunted in civilised man. Both savages and lower 

 animals will find their way back in a "bee-line" through un- 

 known country, to places whence they have been led by tortuous 

 tracks. Why should not this "sense of direction" then guide 

 birds over oceans without landmarks. The case of first migra- 

 tion of young birds (cuckoos and starlings) quoted by Prof. 

 Newton, is, it must be confessed, a problem difficult to solve ; 

 but when the journey has been once made by an individual bird 

 in a flock I cannot see more mystery in the arrival of that flock 

 at their destination than there is in the perfect accord between 

 the hand and the eye of a good shot or a good billiard player. 



We must all concur with Col. Donnelly in desiring further 

 observations, with facility for publication and discussion, and I 

 venture to hope that we .shall see many more papers from Prof. 

 Newton's pen on the subject. E. H. Pringle 



Scientific Club, Savile Row, March 18 



lightly pres.sed by the membrane, and as this pressure may be 

 more or less strong during the action of the apparatus, the latter 

 acts as a microphone of a relatively weak sensitiveness, but 

 which permits the telephone to be spoken to at a distance of 

 several centimetres, and of hearing the ticking of a watch, or the 

 sounds of a musical box with the aid of a carbon microphone. 



The Microtelephone 



Towards the end of last year I got constructed a telephonic 

 apparatus which gives results much superior to those of the 

 ordinary Bell telephone. Its construction is ba.sed on four 

 principles, two of which have not yet been applied to tele- 

 phones : — 



1. The magneto-electric principles of the Bell telephone. 



2. The microphonic principles of Hughes (different quantity 

 of the points of contact). 



3. The principle discovered by Beatson and De La Rive (1845), 

 and which explains the experiments of Messrs. Blyth and Hughes 

 with the speaking microphone (production of sounds by the 

 passage alone of a discontinuous or undulating electric current). 



4. The principle that the intensity of the sound depends on the 

 density of the air in which it is produced. 



All the principles are combined in so simple a manner that the 

 microtelephone differs from the Bell telephone only in the three 

 following points : — 



1. The electric current engendered by the approach or with- 

 drawal of the iron membrane, traversed not only the bobbin, but 

 also the magnet and the membrane itself. 



2. The communication of the current with the vibrating plate 

 of iron is effected by means of two small springs, which are 



3. Three millimetres above the iron membrane is another 

 membrane of caoutchouc (which should not be very fine), and 

 both membranes inclose a layer of air, moderately compressed, 

 which in this way must vibrate, together with the two membranes. 



The microtelephone is regulated once for all, and transmits 

 the feeblest word with a truly perfect precision. 



Julian Ochovowicz 



University, Lember/, Galicia 



Vacuum Tube Phenomena 



Has it been observed that the area of the exposed surface of 

 the negative electrode in a highly exhausted vacuum tube exerts 

 an important influence on the facility with which the discharge 

 takes place? 



I have recently been observing Crookes's molecular shadows 

 with a tube constructed by Mr. J. Marr, of Liverpool, in which 

 one electrode is a flat disk about i inch in diameter, and the 

 other a piece of platinum wire about | inch long. When these 

 electrodes are connected with the terminals of an induction coil 

 capable of giving a 44-inch spark in air, and the contact- 

 breaker arranged so that the shadows can just be seen when the 

 disk is in connection with that terminal which becomes negative 

 when the current in the primary wire is broken, a reversal of 

 the commutator causes the discharge to cease. 



If, now, the coil power be increased by the proper manipula- 

 tion of the contact-breaker, a condition of things is reached in 

 which the dark shadows flash out intermittently, even though 

 the disk is connected with what is called the positive terminal of 

 the induction coil. 



This is evidently caused by the passage of the inverse induc- 

 tion current ; I mean that current which is produced when the 

 circuit of the primary is completed. It thus appears that a 

 condition of things can be obtained in which the effect of the 

 greater electromotive force produced on the breaking of the 

 primary circuit is counterbalanced by the influence of the relative 

 size of the electrodes. 



The above observation appears to be interesting, and as it 

 may possibly be new, I venture to send you an account of it. 



Nottingham, March 8 J. J. H. Teall 



Leibnitz's Mathematics 



Prof. Tait has recently given your readers one mathemati- 

 cian's opinion of Leibnitz as a discoverer. The following 

 extract is serviceable in the same direction, while it has the 

 further merit of attesting to the existence of a still later "vestige 

 of presumption " than has yet been referred to. The extract is 

 from a review by M. Bertrand of Diihring's "Kritische Geschichte 

 der allgemeinen Principien der Mechanik " (Berlin, 1873). M. 

 Bertrand says : — 



Les severites de M. Diihring sont impartiale.s, et I'un des 

 plus grands genies de I'Allemagne semble precisement le plus I 

 maltraite de tous. Les Actes de Leipzig, de 1684, donnerent, 

 est-il dit dans le texte, la premiere publicite a la theorie des 

 fluxions de Newton, et en note, on ajoute : "II n'a pas ete 

 ' possible d'opposer a Leibnitz des preuves completes qui le 



