314 SECTIONAL TRANSACTIONS.— A. 



Referring to the power developments carried out in the Highlands of 

 Scotland, it would have been of great assistance to him had statistics relating 

 to the rivers been available when the works were designed. The schemes 

 were worked out on rainfall data alone. 



The author considers that there should be a central authority under a 

 Government Department to collect the existing data , and to institute, through 

 such subsidiary organisations as may be necessary, the measurement of 

 rivers not yet utilised. 



Wednesday, September 7. 



Prof. J. J. Nolan. — The diurnal variation of the ionisation in the lower 

 atmosphere. 



Miss M. D. Waller. — A demonstration of the maintenance of vibration 

 by the application of cold. 



If a solid block of carbon dioxide be held against a metal, a chattering 

 or singing sound will often be heard, due to vibrations of the latter. This 

 fact is familiar to some of those who handle carbon dioxide commercially. 



Under proper conditions a very loud note may be produced. Thus, for 

 example, let the body to be set into vibration be a somewhat massive tuning- 

 fork of high frequency, e.g. 3,000 p.p.s., and let the solid carbon dioxide 

 be of high density. Then when suitable contact is made between one of the 

 prongs of the fork and the block, the fork may be set into violent vibration 

 which may be maintained for some seconds if the contact be skilfully 

 adjusted. 



Bodies of different shapes (bars, discs, rings, etc.) and of different metals 

 may be similarly excited, and irregularly shaped bodies will sometimes give 

 out much noise. 



In explanation of the phenomenon it would appear that the source of 

 energy for producing the vibrations is the heat which is given up by the metal 

 to the solid carbon dioxide, and that the efficacy of the carbon dioxide in 

 producing vibrations is determined by the fact that it sublimes and that 

 considerable gas pressures are produced during the momentary contacts 

 of the metal with the block. 



Prof. L. S. Palmer. — Short-wave reception zvith frame aerials. 



When a frame aerial receives wireless waves comparable in length with 

 the frame dimensions, the maximum current depends not only upon the 

 tuning, but also upon the ratio of the wave-length to the width and height 

 of the frame. The critical frame dimensions also vary with the angle of 

 incidence of the wave. By considering the interaction between the currents 

 in adjacent parts of the frame, the critical dimensions can be calculated. 

 It is then found that for a frame of any given width there are, within one 

 wave-length, at least two critical heights for which the received current will 

 be a maximum. Furthermore, any increase in the width can be com- 

 pensated by a proper decrease in the height, and vice versa. The greatest 

 current will be produced in those correctly proportioned frames which have 

 the largest area, but zwcreasing the area without maintaining the correct 

 dimensions (depending on the wave-length X and angle of incidence) will 

 cause a c?ecrease of current. Thus the areas of the frame are also critical, 

 and vary from o- 15 X^, 0-50 X^, etc., to 0-24 X^, 0-73 X^, etc., depending on 

 the angle of incidence of the waves. 



