Febeuaky 10, 1899.] 



SCIENCE. 



225 



curves of 125 variables in w Centauri have been 

 obtained. 



Among other matters discussed by Professor 

 Piclcering in his report is the organization of 

 the Observatory. The Harvard College Observ- 

 atory is not, like many other observatories, 

 divided into departments each under an as- 

 tronomer of high grade. The Director himself 

 is in immediate charge of all the departments, 

 in many cases making a daily inspection and 

 planning the work in detail. The assistants 

 become skilful each in a particular work, and 

 three or four times as many can be employed 

 at a given expenditure as under the depart- 

 mental system. The report mentions the ad- 

 vantages and disadvantages of each plan and 

 advises that the plan in operation at Harvard 

 should continue to be followed in one large 

 observatory. The corps of assistants at Harvard 

 and at the Southern Station, in Peru, includes 

 forty persons. 



THJ PLANET DQ. 



This planet has been named Eros. The As' 

 ironomical Journal and Circular 36 of the Har- 

 vard Observatory contain the gratifying an- 

 nouncement that numerous observations of the 

 planet have been found on the Harvard plates 

 in 1894 and 1896. In 1894 the planet was at 

 its most favorable position for observation, and 

 of the 7th magnitude when nearest. Observa- 

 tions have been found extending for more than 

 four months, making it possible to determine an 

 accurate orbit for that opposition alone. Dr. 

 Chandler has undertaken the rigid discussion 

 of all available data, and will bring the calcula- 

 tion down to the 1900 opposition, so that the 

 observations then to be made will be under the 

 best knowledge of the theory of the planet's 

 motion. 



This research has justified the policy of Pro- 

 fessor Pickering in having the whole sky photo- 

 graphed at frequent intervals. That the plates 

 thus accumulating contain a vast amount of 

 material which the future needs of astronomy 

 will utilize is quite evident. That many new 

 facts can be obtained from their examination Is 

 shown by the discovery during the search for 

 the planet Eros of two variables and two stars 

 which are not in the Durchmusterung catalogue. 



besides observations of asteroids previously dis- 

 covered. 



WiNSLow Upton. 

 Brown Univehsity, January 27, 1899. 



NOTES ON PHYSICS. 



SOME RECENT INVESTIGATIONS UPON THE BEC- 

 QOEEEL EAYS. 



Rutherford {Phil. Mag., Jan., 1899), in an 

 important and interesting paper, shows experi- 

 mentally that in a mass of gas exposed to the 

 radiation from uranium, thorium or their com- 

 pounds the following statements hold good: 



1. Charged carriers produced through the 

 volume of gas. 



2. Ionization proportional to the intensity of 

 the radiation and the pressure. 



3. Absorption of the radiation proportional 

 to pressure. 



4. Existence of a saturation current ; i. e., a 

 current passing through the ionized gas, whose 

 magnitude is such that all of the carriers pro- 

 duced by the radiation reach the electrodes. 



5. Rate of combination of the ions propor- 

 tional to the square of the number present. 



6. Partial separation of positive and negative 

 ions. 



7. Disturbance of potential gradient under 

 certain conditions between two plates exposed 

 to the radiation. 



' It is also shown that the radiation given off 

 by both uranium and thorium is complex, con- 

 sisting of two varieties which the author calls 

 a and /3 respectively; /3 being the one of greater 

 penetrative power, while a is the one chiefly in- 

 strumental in causing ionization in gases. The 

 intensity of the a radiation seems to depend 

 chiefly upon the amount of surface of the uran- 

 ium, while the P radiation depends upon the 

 thickness of the layer. 



In Wied. Ann., No. 12, for 1898, Elster and 

 Geitel give an account of a research undertaken 

 by them to test the validity of two suppositions 

 which have been made as to the cause of the 

 Becquerel rays. Madame Curie {Comptes Rendus, 

 CXVI., p. 1101) has suggested that the con- 

 tinuous radiation from uranium, thorium and 

 their compounds may be explained by suppos- 

 ing all space to be filled with a sort of modified 

 Rontgen radiation which possesses the power 



