Intelligence and Miscellaneous Articles. 151 



AMOUNT OF CARBON DIOXIDE IN THE ATMOSPHERE. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



My thanks are due and tendered to Prof. John LeConte for 

 pointing out a numerical error relating to the above which has 

 crept into my paper on " Carbon Dioxide as a Constituent of the 

 Atmosphere," published in the number of your Journal for No- 

 vember last. It is pleasing to be able to add, however, that the 

 main conclusions and arguments of that paper are not thereby 

 affected. The mistake arose apparently by making use in some 

 unaccountable manner of the formula for a prolate spheroid instead 

 of that for an oblate one. Making the correction and recalculating 

 on the basis of 3 vols, of C0 2 per 10,000 (which all recent inves- 

 tigations show to be nearer the truth than 4), we obtain 



"Weight of C0 2 in atmosphere = 2420 billions of kilogrammes 

 nearly. 



The great difference between this number and that given by the 

 older chemists and stated in text-books will, I think, justify the 

 conclusion drawn in my paper, that the generally received idea of 

 the amount of C0 2 in the atmosphere is much too great. 



I am, Gentlemen, 



Tour obedient servant, 



Ebnest H. Cook. 



EXPERIMENTS ON THE DIRECT PHOTOGRAPHY OF SOUND- 

 VIBRATIONS. BY PROF. BOLTZMANN. 



A small thin platinum plate was attached perpendicularly to the 

 centre of a thin iron plate, which, as in the telephone or phonograph, 

 was fixed on a wall-piece. It was first ascertained that the small 

 platinum plate really repeated approximately unchanged the vibra- 

 tions of the sound that arrived in the capsule. For this purpose a 

 second small platinum plate was fixed immovably in the vicinity of 

 the first. The resulting fine slit between the two was brought into 

 the focus of a collecting-lens, upon which sunlight fell. After 

 passing through the slit, the rays reached a Breguet selenium cell, 

 which, together with two telephones, was inserted in the closing 

 circuit of twelve Leclanche cells. Single sounds and words spoken 

 into the mouthpiece could be heard most distinctly in the telephones. 

 When the rays, after issuing from the slit, were rendered as nearly 

 as possible parallel, and intercepted at a greater distance by a large 

 collecting-lens to be concentrated upon the selenium cell, the appa- 

 ratus could also be employed as a photophone. 



After these preliminary experiments, intense sunlight was again 

 concentrated upon the vibrating platinum plate; and then, by 



