lis Progress in Physics. [January, 



The spectrum of the light during the magnificent Auroral display of the 24th 

 and 25th of October was obtained by several observers. From the following 

 abstract of their accounts it will be seen that there is a general uniformity in 

 the results; the presence of hydrogen appearing to be established. 

 Professor A. H. Church, of the Royal Agricultural College, writing to the 

 " Chemical News," says that he was able to observe the spectrum of the aurora 

 as seen at Cirencester. He saw a steady yellowish green line, and frequently 

 a brilliant red line near that of calcium. A pale line was also seen in the 

 green, and a more definite one in the blue — these last not being constant in 

 occurrence. 



A correspondent of " Nature," " T. F.," observing at Torquay, saw four lines 

 in the rosy portion, and one in the greenish ; one strong red line near C, one 

 strong pale yellow line near D, one paler near F, and one still paler beyond. 

 The C line was very conspicuous, and was intermediate in position and colour 

 to the red of the lithium and calcium. His opinion is that there were two 

 spectra superposed ; the red portions showing the four lines (probably hydrogen) 

 and the greenish only one, near D. 



Mr. W. B. Gibbs saw two bright lines ; one, a red, looking like the C hydrogen 

 line, and one a greenish gray. 



Mr. Elger saw a red band near C, a bright band near D, a faint and rather 

 nebulous line, supposed to be near F, and another very faint line between the 

 latter two. 



Mr. H. R. Proctor saw a brilliant red line more refrangible than the hydrogen 

 C line. 



Mr. J. R. Capron saw a line in the red very much like the lithium line, and 

 a line in the light green like one of the lines from the larger nebulas. 



It may be of interest to compare these observations with those of other 

 observers made previously. J. A. Angstrom found the light of the aurora to 

 be almost monochromatic, consisting of a single bright line less refrangible 

 than the red calcium lines. With a wide slit, traces of three other bands were 

 seen. Professor Winlock found the spectrum to consist of four green lines and 

 one blue line. Three of the green lines coincided with lines seen in the 

 spectrum of the corona as observed by Professor Young during the total solar 

 eclipse of August, 1869. 



Microscopy. — A correspondent of the " American Naturalist " makes the old 

 complaint as to the insecure mode by which dry objects are commonly mounted. 

 Paper, paste, and gum are, as usual, the origin of all the mischief, affording no 

 protection against damp, scarcely keeping out dust, and favouring the growth 

 of numerous fungi, which, sooner or later, spoil the preparation. He suggests, 

 as the only remedy, a steady refusal to purchase objects so mounted. This 

 state of things is just as common in England ; the majority of dry objects being 

 mounted in the above well-known manner. To those who merely require a 

 few showy preparations to gratify the taste of the moment for sensational 

 objects, these defects may be of little importance, but to the student the storing 

 of objects for reference at, possibly, a very distant period, is a matter of the 

 utmost consequence. No dry preparations should be tolerated unless secured 

 in air-tight cells, and every precaution should be taken not only to exclude 

 damp, but also not to include it ; the object should not only be thoroughly 

 dried, but the mounting should be done in a dry atmosphere ; there is no reason 

 why as much pains should not be taken to keep the damp out of dry objects as 

 there is to retain the liquid in the cell in the case of fluid mountings. Our 

 microscopical cabinets ought to be available for the use of the observers of at 

 least the next century. 



Mr. T. Greenish has examined microscopically the various articles sold as 

 lint. The result appears to be, that those labelled " Lint " consist entirely of 

 cotton, while, with one exception, those described as " Flax lint " contain more or 

 less cotton, but by an ingenious arrangement of the materials the linted surface 

 is composed almost entirely of flax. There is an idea prevalent that cotton 

 forms an extremely bad application to sores, causing great irritation, and linen 



