Physics and Astronomy. 311 



On the taking up of water vapor by solid bodies y by Dr. T. 

 Ihmori. 



On xoater of crystallization of dissolved cobalt salts y by Jacob 

 Kallir. 



An answer to IV. Voigt's remarks upon elliptical polarization 

 of the reflected light of transparent bodies; by W. Wernicke. 



Projection of the true image of a vibrating string y by J. 

 Puxuj. 



Answer to the remarks of Franz Koldcek on the freezing 

 point ; by Robert von Helmholtz. 



Water of Crystallization y by W. Mtjxler-Erzbach. 



On the height of clouds y by W. Kohlrausch. — The author 

 noticed a peculiar cloud and measured its height, obtaining a 

 height of sixty kilometers. j. t. 



2. The production, properties and uses of very fine threads. — 

 The production of extremely fine threads of glass, quartz and 

 other materials has been brought to a high degree of perfection 

 by Mr. C. V. Boys. The method which he found most satisfac- 

 tory in its results was the following : a fragment of drawn out 

 glass was attached by sealing wax to the tail of an arrow made 

 of a piece of straw a few inches in length; the glass was heated 

 to a high temperature in the middle and while the end was held 

 in the fingers the arrow was projected by a cross bow of pine 

 held in a vise and with a trigger that could be pulled by the 

 foot. With every successful shot the thread was continuous from 

 the piece held in the hand to the arrow 90 feet off, a glass thread 

 90 feet long and xo,Voff mca m diameter being obtained. The 

 diameter was almost perfectly uniform for the greater part of the 

 length. Instead of holding the glass tail in the hand, a little 

 bead of glass may be fused on the end and, when the arrow is 

 shot, the inertia of the bead is sufficient to draw out the thread 

 in the same way. 



The author has also experimented upon a number of minerals 

 and found that while some behave like glass, others will not draw 

 at all being either perfectly fluid like water or when cooler per- 

 fectly rigid. Thus corundum, hornblende, zircon, rutile, cyanite, 

 fluorite will not draw at all; on the other hand emerald and 

 almandine will draw but care is needed to obtain the proper tem- 

 perature. Orthoclase draws readily, but quartz though trouble- 

 some and requiring more force yields remarkably successful 

 threads of extreme minuteness, in some cases tapering down to a 

 size beyond the power of the microscope to resolve. These 

 minute threads have some peculiar properties which the author 

 proposes to investigate, they are highly elastic and it is suggested 

 that they may be advantageously used for torsion-threads. They 

 may also be preferable to spicier lines for the cross wires in the 

 eye-pieces of microscopes and other instruments. — Phil. Mag., 

 xxiii, 489. 



3. Photography by Vital Phosphorescence.— ~Dn. John Van- 

 sant has continued his experiments in photography by phospho- 



