286 



NA TURE 



[July 22, 1897 



vibrating fork as a source of sound. The energy resident in the 

 fork at any time may be deduced from the amplitude as 

 observed under a microscope. From this the rate at which 

 •energy is emitted follows when we know the rate at which the 

 vibrations of the fork die down (say to one-half). In this way 

 the distance of audibility may be reduced to 30 metres, and the 

 results are less liable to be disturbed by atmospheric irregu- 

 larities. If s be the proportional condensation in the waves 

 which are just capable of exciting audition, the results may be 

 expressed : — 



s = 6'o X lo' 

 J = 4-6 X 10' 

 J = 46 X 10" 



c' I frequency = 256 



/ „ =384 



^ I >) = 512 



showing that the ear is capable of recognising vibrations which 

 involve far less changes of pressure than the total pressure out- 

 standing in our highest vacua. 



In such experiments the whole energy emitted is very small, 

 and contrasts strangely with the 60 horse-power thrown into the 

 fog-signals of the Trinity House. If we calculate according to 

 the law of inverse squares how far a sound absorbing 60 horse- 

 power should be audible, the answer is 2700 kilometres ! The 

 conclusion plainly follows that there is some important source of 

 loss beyond the mere diffusion over a larger surface. Many 

 years ago Sir George Stokes calculated the effect of radiation 

 upon the propagation of sound. His conclusion may be thus 

 stated. The amplitude of sound propagated in plane waves 

 would fall to half its value in six times the interval of time 

 occupied by a mass of air heated above its surroundings in 

 cooling through half the excess of temperature. There appear 

 to be no data by which the latter interval can be fixed with any 

 approach to precision ; but if we take it at one minute, the con- 

 clusion is that sound would be propagated for six minutes, or 

 travel over about seventy miles, without very serious loss from 

 this cause. 



The real reason for the falling off at great distances is . doubt- 

 less to be found principally in atmospheric refraction due to 

 variation of temperature, and of wind, with height. In a normal 

 state of things the air is cooler overhead, sound is propagated 

 more slowly, and a wave is tilted up so as to pass over the head 

 of an observer at a distance. [Illustrated by a model.] The 

 theory of these effects has been given by Stokes and Reynolds, 

 and their application to the explanation of the vagaries of fog- 

 signals by Henry. Progress would be promoted by a better 

 knowledge of what is passing in the atmosphere over our heads. 



The lecture concluded with an account of the observations of 

 Preyer upon the delicacy of pitch perception, and of the results 

 of Kohlrausch upon the estimation of pitch when the total 

 number of vibrations is small. In illustration of the latter sub- 

 ject an experiment (after Lodge) was shown, in which the 

 sound was due to the oscillating discharge of a Leyden battery 

 through coils of insulated wire. Observation of the spark proved 

 that the total number of (aerial) vibrations was four or five. The 

 effect upon the pitch of moving one of the coils so as to vary the 

 self-induction was very apparent. 



UNIVERSITY AND 'EDUCATIONAL 

 INTELLIGENCE. 



Among other bequests, the late Mrs. Muspratt, widow of Dr. 

 Sheridan Muspratt, left by will the sum of 500/. to University 

 College, Liverpool. 



Dr. E. S. MacBride, Fellow of St. John's College, and 

 Demonstrator in Animal Morphology in the University of Cam- 

 bridge, has been appointed to the newly-founded chair of 

 Zoology in the McGill University, Montreal, Canada. 



The University of Leipzig has conferred the honorary degree 

 of doctor of medicine upon Dr. Simon Schwendener, professor 

 of botany at Berlin ; Dr. W. Hempel, professor of chemistry at 

 Leipzig ; and Dr. W. Hittorf, professor of physics in the 

 Munster Academy. The same University has conferred the 

 honorary degree of doctor of philosophy upon Dr. A. Fick, pro- 

 fessor of physiology at WUrzburg ; Dr. W. His, professor of 

 anatomy at Leipzig ; and Dr. K. von Leibermeister, professor 

 of anatomy at Tiibingen. 



We learn from the Lancet that Prof. Engelman, in taking 

 over the late Dr. du Bois Reymond's chair of Physiology at 

 Berlin, is arranging certain changes in the Physiological In- 



NO. 1447. VOL. 56] 



stitute and its four departments. The first, for microscopical 

 and biological work, will remain under the charge of Prof. 

 Fritsch. Similarly, the second, for chemical physiology, will 

 continue under its present director, Prof. Thierfelder. The 

 third, for special physiology, will be greatly enlarged, and the 

 professor himself will take part in its work in conjunction with 

 the present director. Dr. Immanuel Munk. The fourth depart- 

 ment, for physical physiology, will also be largely increased ; 

 it will be called the Department for the Physiology of the 

 Sensory Organs, and will remain under the direction of Prof. 

 Konig. In addition to extensive new buildings, the supply of 

 apparatus will be largely augmented. The lectures will be 

 given by the professor in a course running through two semesters, 

 but during the last four weeks in the summer Prof. Konig will 

 lecture on the sensory organs, and during the first four weeks 

 of the winter Prof. Thierfelder will lecture on physiological 

 chemistry. 



SCIENTIFIC SERIALS. 



American yournal of Science, July. — Pressure coefficient of 

 mercury resistance, by A. de Forest Palmer, jun. By means of 

 Barus's screw compressor, a thread of mercury was subjected to 

 a series of pressures up to 2000 atmospheres. If R is the re- 

 sistance under any pressure, Rj that under atmospheric pressure, 

 P the pressure, and & the increment for one atmosphere, then 

 R = Ro ( I + ;8P). The result of the measurements is that 

 /3 = - o '0000332 - 5 X \o"^t. This differs only very slightly 

 from the value obtained by Barus. —An interesting case of con- 

 tact metamorphism, by H. W. Fairbanks. Black Mountain is 

 the highest peak of the El Paso range, a spur of the Sierra 

 Nevada mountains extending eastwards into the Mogave desert. 

 The mountain owes its name to the dark lava which covers it. 

 The underlying rocks constitute a part of an extensive series of 

 sedimentary beds exposed for many miles along the northern 

 slope of the El Paso range. The strata have been considerably 

 disturbed and faulted, and in one of the caiions have been in- 

 truded by two dykes. One of these is 14 feet across, and is a 

 holocrystalline olivine diabase.— The adjoining rock has been 

 strikingly metamorphosed. The thickness of the band of altered 

 tufa is about 2 feet where it is best exposed. The light- 

 coloured soft rock has been baked to a dark, hard and very firm 

 one, the slabs of which give forth a ringing sound when struck. 

 The layer is not massive, but breaks up into slate-like slabs. 

 The partings are probably due to contraction on cooling. — The 

 tin deposits of Temescal, South California, by H. W. Fairbanks. 

 The tin deposits lie nearly in the centre of a rudely semicircular 

 area of granite, which is fissured along almost innumerable lines 

 in which a black vein matter is deposited. The veins vary from 

 one-fourth to a few inches in thickness, and consist of tourmaline 

 and quartz, with which the tin ores are loosely associated. They 

 occur in two forms : the common variety is either massive and 

 brownish, or in clear reddish-brown crystals lining cavities ; the 

 less common variety is that of " wood tin," which appears un- 

 crystallised and in the form of thin layers.— Electrosynthesis, 

 by W. G. Mixter. Mixtures of various gases were subjected to 

 a feeble alternate discharge in a special form of eudiometer, in 

 which the terminals consisted of glass surfaces holding water on 

 the other side. Under these circumstances, dry carbonic oxide 

 and oxygen slowly combine. Ethylene and oxygen are partly 

 converted into carbon dioxide and water. Acetylene and oxygen 

 are wholly converted into the same. The molecular changes are 

 analogous to those occurring in synthesis effected by heat or light 

 where combination takes place at a temperature far below that 

 at which the gaseous molecules dissociate. 



The Rendiconti del Reale Istitiito Lombardo, which is 

 devoted to both literary and scientific subjects, contains in 

 recent numbers the following papers of physical interest : — Prof. 

 Aurelio Mauri (xxx. , vii.) describes a new potentiometer, and 

 gives an account of observations of the electromotive forces of 

 Clark's cell, and of a new form of element involving the use of 

 acetate of mercury and acetate of zinc. In the next number 

 (xxx., viii.) he gives tables of the electromotive forces of 

 elements involving various salts. In a later number (xxx., x.) 

 Prof Paolo Cantoni describes certain phenomena connected with 

 the charging of a condenser, and which on starting or stopping 

 the electromotor give rise to sudden repulsions of the plates 

 from the intervening dielectric, followed by attraction. These 

 phenomena, the author considers, are the outcome of temporary 



