METEOROLOGY 287 



good starting points for those at work on the theory of this apparatus. 

 (Nature, xxvii, p. 370.) 



111. [Ahnost the only way to get a physically clean surface of glass 

 is by heating it in concentrated sulphuric acid, to which a little nitric 

 acid has been added, and then heating, after washing with pure water 

 to remove the acid ; such a glass surface exposed to the air for a short 

 time is generally imi)erfectly wetted by water. Tbe hygroscopic prop- 

 erties of physically clean surfaces probably need full elucidation be- 

 fore the dew-point apparatus can become a jierfectly accurate jihysical 

 a])paratus.] 



112. H. Kai)eller has modified the construction of his combined maxi- 

 mum and minimum thermometer so as to secure the greatest simplicity 

 and still accomplish a transportable, safe, and economical instrument. 

 {Z. 0. G. M., XVIII, p. 225.) 



113. Dr. E. Lenz described a method of utilizing the telephone for 

 the measurement of temperatures at distant points which is applicable 

 up to distances of 25 kilometers. {Nature, xxx, p. 340.) 



114. Prof. William Forster describes some results of investigations 

 into accuracy of thermometers carried out by the German Normal Stand- 

 ards Commission. Passing from the errors of the mercurial thermome- 

 ter he considered the air thermometer, and showed that the chemical 

 composition of the glass bulb affects even that, as experiments showed 

 that all gases are more or less absorbed by the glass, and the more so 

 the longer the gas remains in contact with the inner wall of the bulb, 

 thus affecting the result among the hundredths of a degree. {Nature, 

 xxx, p. 652.) 



115. Prof. R. Weber has made a most laborious examination of the 

 influence of the chemical constituents of the glass upon the depression 

 of the freezing point of thermometers ; he finds the best results with a 

 pure potash alkaline glass free from soda, and it is probable that he will 

 be able to construct a special glass in which the troublesome source of 

 error is reduced to a minimum. (D. 3f. Z., i, p. 286.) 



116. O. Pettersson, of Stockholm, proposes improved methods for 

 measurement of heat, namely, that the measurements should be made 

 at a constant temperature and that the ice calorimeter of Bunsen should 

 be improved by directly transforming the heat into work. In order to 

 maintain a constant temperature he had recourse to a thermometric 

 combination which proved unsatisfactory and substituted a method of 

 measuring the work done by isothermic expansion of air. In this way he 

 is able to measure the mechanical effect of radiations the caloric energy 

 of which was only 0.08 gramme- calorie per minute. {Nature, xxx, p. 

 321.) 



117. Mr. G. M. Whipple, of Kew, communicates preliminary results 

 as to the discrepancies between various black bulbs in vacuo; he finds 

 that among other things the effect of successively increasing the tliick- 

 jiess of the coat of lamp-black is to raise the temperature, and that the 



