14 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 13, No. 1 
which show that many of the non-radioactive elements may exist in two or 
more forms having practically identical chemical and spectroscopic properties 
but with different atomic weights. Such substances are called isotopes, 
because they occupy the same place in the periodic table of the elements. 
The speaker described his mass spectrograph, which he has employed with 
great effectiveness in the detection of isotopes. The positively charged ions 
of the element under examination are projected first through an electric 
field and then through a magnetic field, impinging finally upon a photo- 
graphic plate. If the element under examination consists of two isotopes, 
two lines or bands appear in the spectrum, the position of the line being 
determined by the mass of the isotope. Thus, boron (atomic weight 10.9) 
has two isotopes with masses 10 and 11; magnesium (atomic weight 24.32) 
has three isotopes with masses 24, 25, and 26. Fifteen or more of the non- 
radioactive elements have thus been shown to be isotopic mixtures, while 
others give no evidence of such complexity. 
An excellent account of Dr. Aston’s brilliant work in this field, for which 
he has recently been awarded the Nobel prize, may be found in his book 
on Isotopes. 
168TH MEETING 
The 168th meeting of the Acapremy was held jointly with the American 
Institute of Electrical Engineers (Washington Section) in the Assembly 
Hall of the Cosmos Club, the evening of Thursday, May 18, 1922. Dr. A. 
Van Dyck, of the General Electric Company, delivered an address on The 
vacuum tube in present day radio. 
Doctor Van Dyck first outlined the fundamental relations between current 
and voltage within the electron tube or ‘‘triode,’’ and showed how the presence 
of a minute charge of electricity on the grid could control the flow of much 
larger currents to the plate. Such tubes are useful as rectifiers, detectors, 
amplifiers, and modulators. He then showed a large number of slides illus- 
trating the astonishing development of the electron tube during the past 
few years, and the huge scale on which it is now being applied in radio- 
telegraphy and -telephony, as well as to the extension of the range of wire 
telephony. Many of the slides illustrated the elaborate equipment installed 
in the high-power radio-telephone broadcasting stations. 
169TH MEETING 
The 169th meeting of the Acapemy was held jointly with the Medical 
Society of the District of Columbia and the Society of American Bacteri- ~ 
ologists Washington Branch) in the Auditorium of the Medical Society, 
the evening of Tuesday, September 19, 1922. Dr. K. F. Meyer, Acting 
Director of the Hooper Foundation, delivered a lecture, entitled, A summary 
of the studies on B. botulinus conducted at the Hooper Foundation for Medical 
Research, University of California. 
The address was illustrated with lantern slides, and included a description 
of the methods employed and a statement of the results obtained in an 
intensive study of this subject lasting more than two years Among the 
subjects discussed were: Distribution of B. botulinus in nature; the con- 
ditions under which it will grow; the biochemical activities of B. botulinus; 
the relation of toxin formation to the growth curve of the micro-organism 
and to physical evidence of spoilage of the food; heat resistance of B. botu- 
