October 80, 1885.] 



8GIE]SrCE. 



387 



liroublesome problem of how to treat pamphlets in 

 professional libraries.'" Edward S. Holden. 



Washburn observatory, Oct. 19. 



An attempt to photograph the corona. 



By a slip of the pen in my communication on this 

 subject in the last number of Science, I gave the 

 references to two previous letters as April 29 and 

 April 13. These should read May 29 and May 15. 

 By a typographical error I am made to refer the ob- 

 servations on the light of the corona to Prof. S. P. 

 Xangley. The observations were made by his 

 brother. Prof. John W. Langley. 



According to his observations, as we have already 

 seen {Science, August 14), the light of the corona 

 within 1' of the sun's disk is six times that of the full 

 moon ; which, according to my observations, would 

 be one-fiftieth that of our atmosphere in this vicin- 

 ity. Professor Bonney states, (The sun, p. 229.) that 

 a brilliancy of only one sixty fourth would be suffi- 

 •cient to render the planets visible. Therefore, even 

 if the atmospheres of Mercury and Yenus produced 

 Tio visible effect at all, the facts would still sustain 

 Professor Langley 's observations. 



Wm. H. Pickering. 



Recent Proceedings of Societies. 



Philosophical society, Washington. 

 Oct. 24. — Mr. H. A. Hazen read a paper on con- 

 densing hygrometers and sling psychrometers. As 

 preliminary to the paper proper, Mr. Hazen gave the 

 results of some interesting experiments which he had 

 made with a view of determining the most desirable 

 distance between the lines upon the stem of a ther- 

 mometer, in order that tenths of degrees may be esti- 

 mated with the greatest accuracy. He had made a 

 considerable number of trials, in which he had first 

 estimated the fractions, and afterwards measured 

 them by the use of a vernier. The results seemed to 

 indicate that there was a length of division on which 

 the estimation of tenths might be made with greater 

 precision than on one either longer or shorter. Mr. 

 Hazen did not consider, however, that his experi- 

 ments were sufiiciently numerous to enable him to 

 determine this with certainty. On directly address- 

 ing himself to the subject of his paper, he called 

 attention to the various forms of Eegnault's condens- 

 ing hygrometer, which had appeared from time to 

 time, briefly discussing the advantages and disad- 

 vantages of each. He spoke of the numerous 

 methods which have been devised for ventilating the 

 psychrometer, and expressed his belief that the form 

 known as the 'sling' was the best of all. Experi- 

 ments made by using both of these instruments for 

 the purpose of determining the value of the constant 

 A in the common psychrometric formula were de- 

 scribed, and the effect of elevation was considered. 

 Mr. Mendenhall exhibited one of Sir Wm. Thom- 

 son's long-range voltmeters, which had been recently 

 imported by the chief signal officer. A small 

 cylinder of soft iron hangs upon tlie short arm 

 of an index lever, which is so balanced as to 

 be practically in indifferent equilibrium. The 

 iron is surrounded, without contact, by a coil 

 which is so wound that the strength of the field 

 produced by the passage of a current increases 

 from the lower to the upper end of the coil. As the 

 pull on the soft iron is proportional to rate of^the 



change of the square of the strength of field, and as 

 this rate diminishes from the lower to the upper end 

 of the coil, the force exerted on the cylinder will de- 

 pend at once on the current strength and on its 

 position in the coil. By hanging a small non- 

 magnetizable weight to the iron by means of a hook 

 projecting from the lower end, this force is made to 

 be constant when equilibrium exists, so that when 

 the current strength varies, the position of the iron 

 cylinder changes, and this position is read off on a 

 scale at the extremity of the long arm of the lever. 

 The great merits of the instrument are its constancy 

 and the ease with which it may be adapted to the 

 measurement of potentials differing greatly in mag- 

 nitude. — Mr. Mendenhall also made some remarks 

 upon instruments and measurements of the so-called 

 re-action time, originating in the exhibition of these 

 instruments by Dr. Matthews at a previous meeting 

 of the society. He referred to a paper upon the sub- 

 ject, which he had published in the Avnerican journal 

 of science, in 1871, in which instruments and methods 

 are described identical in many respects with those 

 recently exhibited. Eesults were given, showing 

 the time occupied in responding to a signal, which 

 was a flash of light, the appearance of a card, a sound, 

 or a blow upon the hand or head, and also the time 

 consumed in the simplest processes of reasoning. 

 These times were, in general, shorter than those 

 recently obtained by Dr. Matthews, but differences 

 in the manner of conducting the experiment will 



doubtless account for this, Mr. Harkness discussed 



the flexure of transit instruments. He pointed out 

 its dependence on the form of the instrument, and 

 also that its amount might be expressed as the sum 

 of two different functions of the zenith distance. The 

 nature of one of these functions can be readily ascer- 

 tained ; but unfortunately that of the other is un- 

 known, and, in a general sense, impossible to deter- 

 mine. For certain classes of instruments it might be 

 ascertained by the assumption of accuracy in tables of 

 star positions, but Mr. Harkness declared that he 

 knew of no way by means of which the problem 

 could be completely solved for the astronomical ob- 

 servatory. Discussion of this paper was prevented 

 by the operation of a rule of the society, in obedience 

 to which it closes its session promptly at ten o'clock. 

 In a general way, it cannot be denied that a strict 

 compliance with this rule has many advantages. A 

 visitor to the society may be certain that he will not 

 be obliged to wait for more than a minute or two 

 after eight for its beginning, and, however uninterest- 

 ing to him the dissertations to which he listens may 

 be, he may console himself by the reflection that a 

 limit is set to their duration. 



Academy of natural sciences, Philadelphia. 



Oct. 20. — A communication was read from Mr. W. N. 

 Lockington on the causes of elevation and depression 

 of the earth's surf ace, with special regard to the setting 

 of loosely compacted sediments by pressure of super- 

 incumbent beds. Some have supposed that the great 

 beds of ice which encumber the poles bear down the 

 surface rocks of the region by their weight. It is, of 

 course, possible that a downward movement of the 

 earth's crust may be caused by strata piled upon it ; 

 but as the earth's contraction is a sufficient cause for 

 all such movements, it is useless to postulate other 

 causes. The extreme of possible compactness, how- 

 ever, is reached in the sediments themselves by the 



