Chemistry and Physics. 253 



This coincidence may be only accidental. Schuster has employed 

 a criterion which depends upon a supposed harmonic relation be- 

 tween the lines of a spectrum. Mr. Love employs a method 

 of discrimination based upon the law of error. The differences 

 between the wave-length of the lines compared are arranged in 

 groups, each group containing those observations, the errors of 

 which lie within certain narrow limits. The number of observa- 

 tions in each group is then plotted as an ordinate of a curve, the 

 average error of the group being the abscissa. This curve is then 



c 2 x i 

 compared with the law of error y = as— . To show the appli- 

 cability of the method, various curves are given, notably those 

 'due to observations on cerium and the spectrum of water. — Phil. 

 Mag., Jan. 1888, pp. 1-6. j. t. 



14. Influence of thickness and luminosity of light-producing 

 layers, upon the character of spectra. — Certain authors, notably 

 Wullner in his work on Experimental Physics, maintain that line 

 and banded spectra can be made interchangeable by modifying 

 the pressure of the gases or increasing or diminishing the extent 

 of the layer which is made luminous by electrical discharges. 

 Ebeet, by a series of experiments, is brought to the conclusion 

 tbat the experiments adduced by Wullner and other writers, 

 merely show that banded spectra can be reduced to line spectra 

 by diminishing the illumination. No increase or diminution of 

 density or thickness of luminous layers can account for the change 

 of one class of spectra with another. This change must be rather 

 attributed to a change in the molecular grouping. — Ann. der 

 Physik und Chemie, No. 1, 1888. j. t. 



15. On the measurement of force of gravitation. — The deter- 

 mination of the force of gravitation by means of a pendulum, it 

 is well-known, requires great skill and the employment of many 

 corrections. In a note presented to the Academy of Science, M. 

 Defeoeges shows that we can eliminate the effects of the sup- 

 port and that due to the curvature of the knife-edges by making 

 use of two pendulums which oscillate within the same limits of 

 amplitude upon the same support and the same knife edges. 

 These pendulums have the same weight, but are of different 

 lengths. Their centers of gravity are similarly placed in regard 

 to the sides of the knife-edges. — Comptes Pendus, Jan. 9, 1888, 

 p. 126. J. t. 



16. Influence of temperature on Magnetization. — In studying this 

 subject, M. Ledeboer made use of the novel plan of placing the 

 bars of iron or steel in platinum spirals which were heated to suit- 

 able temperatures by means of an electrical current. The soft 

 iron examined by M. Ledeboer, lost its magnetism entirely at 770° 

 C and had barely any at 750° C. In a recent study upon the spe- 

 cific heat of iron at high temperatures, M. Pionchon has shown 

 that iron undergoes a change of state between 660° and 720°. 

 Iron loses its magnetic properties also between 680° and 770°. 

 M. Ledebper calls attention to this remarkable fact. — Comptes 

 Pendus, Jan. 9, 1888, p. 129. j. t. 



