88 Scientific Intelligence. 



field is excited the filament moves out of the field and the move- 

 ment is read by a microscope. The author was led to devise the 

 instrument from a consideration of the elements which enter into 

 the law for the normal sensitiveness of a galvanometer. It was 

 seen that a mirror, however small, limited the possible sensitive- 

 ness. The quartz fiber was stretched between the poles of a mag- 

 net of 12'5 cm height, which enclosed a field of from 20,000 to 

 23,000 c. g. s. The poles are bored in order to light the fiber 

 and also to allow the use of a microscope. By means of a slit at 

 right angles to the axis of this boring, it was possible to photo- 

 graph the excursions of the fiber under varying currents. Photo- 

 graphs of these oscillations are given. The microscope employed 

 magnified 660 times. The period of swing is very short; in a 

 case mentioned by the author only 0*004 sec. The sensitiveness 

 is from 100 to 200 times that of the most sensitive instrument 

 (Panze galvanometer of Rubens) hitherto constructed. The 

 instrument is not affected by jars and vibrations to which other 

 galvanometers are subject, and would seem to be of great use in 

 the detection of minute currents, or rapidly varying currents, 

 which are studied in physiological investigations. — Ann. der 

 Physik, No. 13, 1903, pp. 1059-1071. J. T. 



8. The Magnetic Properties of Systems of Corpuscles describ- 

 ing Circular Orbits. — This paper by Prof. J. J. Thomson is 

 mathematical and not experimental. The problems discussed are : 



(1) The magnetic field due to a number of negatively electrified 

 corpuscles situated at equal intervals round the circumference of 

 a circle and rotating in one plane with uniform velocity round its 

 center. 



(2) The effect of an external magnetic field on the motion and 

 periods of vibration of such a system. 



These problems are met with when we attempt to develop the 

 theory that the atoms of the chemical elements are built up of 

 large numbers of negatively electrified corpuscles revolving around 

 the center of a sphere filled with uniform positive electrification. 

 The mathematical analysis shows that when the velocity of the 

 particle is small compared with V, the velocity of light, the rate 

 at which energy radiates, diminishes very rapidly as the number of 

 particles increases. It is also shown that a body whose atoms 

 contain systems of rotating particles is not necessarily magnetic, 

 and that we cannot explain the magnetic or diamagnetic proper- 

 ties of bodies by the supposition that the atoms consist of 

 charged particles describing closed periodic orbits under the 

 action of a force proportional to the distance from a fixed point. 

 We cannot explain the magnetic properties of bodies by means 

 of charged particles describing, without dissipation of energy, 

 closed orbits. When there is dissipation of energy the particles 

 may possess magnetic properties. 



In discussing this point, Thomson remarks that if the energy of 

 projection were derived from the internal energy of the atom, 

 there would be a continual transference of energy from the atom 



