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fresh strontia was thrown in. Two dark lines were seen in the extreme red, which proved to be the potassium lines reversed (wavelengths 7,670 and 7,700).

With a mixture of barium and potassium carbonates the line with wave-length 5,535 was strongly reversed, and that with wave-length 4,933 distinctly so. When barium chlorate was dropped into a crucible, the four lines with wave-lengths 4,553, 4,933, 5,535, and 5,518, were reversed, and as they remained so for some time, it is probable that the action of the oxygen of the chlorate had nothing to do with the result. The last-named line (5,518) was the least strongly reversed.

To observe particularly the effects of potassium a mixture of lime and potassium carbonate previously ignited was thrown in. The violet lines of potassium, wave-length 4,044, came out immediately as a broad black band, which soon resolved into two narrower dark bands having wave-lengths nearly 4,042 and 4,045. On turning to the red end the two extreme red lines were both seen reversed. No lines of potassium between the two extremes could be seen reversed, but the group of three yellow lines were all expanded though not nebulous, and other lines in the green were seen much expanded. These observations on potassium were more than once repeated with the same results.

Using sodium carbonate only the D lines were seen reversed though the other lines were expanded, and the pairs in the green had each become a very broad nebulous band, and D almost as broad a black band. When sodium chlorate was dropped into a crucible, the pair of lines with wave-lengths 5,681, 5,687, were both momentarily reversed, the latter much more strongly than the former.

When a very little charred rubidium tartrate was put in, the two violet lines were sharply reversed, appearing only as black lines on a continuous light background. Turning to the red end, the more refrangible of the two lines in the extreme red (wave-length 7,800) was seen to have a decided dark line in the middle, and it continued so for some time. The addition of more rubidium failed to cause any reversal of the extreme red line, or of any but the three lines already mentioned.

On putting some lithium carbonate into the crucible, the violet line of lithium appeared as a nebulous band, and on adding some aluminium this violet band became enormously expanded, but showed no reversal. The blue lithium line (wave-length 4,604) was well reversed, as was also the red line, while a fine dark line passed through the middle of

orange line. On adding now a mixture of aluminium filings, and carbonates of lithium and potassium, the red line became a broad black band, and the orange line was well reversed. The green line was exceedingly bright, but not nebulous or reversed, and the violet line still remained much expanded, but unreversed. With regard to the

green lithium line, we may remark that we have no doubt whatever that it belongs to lithium, and that there must have been some


mistake in Thalén's observation, which ascribed it to cæsium. We have never detected this line with cæsium, which, on the other hand, seems always to give the characteristic blue lines, both in the spark and in the flame, as well as to give the same lines reversed when its vapour is used as an absorbent.

When metallic indium was introduced into the crucible, both the lines with wave-lengths 4,101 and 4,509 were at once seen strongly reversed, and so continued for some time. No other absorption line of indium could be detected.

It is apparent that the expansion of lines, so often observed when fresh materials are introduced, must be ascribed to increase in the density of the vapours, not to any increase of temperature. Moreover, the length of tube which reaches a very high temperature in the experiments above described is very short in the lime crucibles, and still shorter in the carbon crucibles, so that the reversing layer is also short in many cases. We are, therefore, directing our attention to the means of heating up a longer length of the tubes, either by introducing oxyhydrogen jets, or additional electric arcs one above another; and also to the introduction of reducing gas (hydrogen or carbonic oxide) to counteract the oxidising action of the air which is drawn in through the lateral openings.

The curious behaviour of the lines of different spectra with regard to reversal has induced us to compare the bright lines of the chromosphere of the sun, as observed by Young, with those that are reversed in our crucibles. It is well known that some of the principal lines of metals giving comparatively simple spectra, such as lithium, aluminium, strontium, and potassium, are not represented amongst the dark lines of Fraunhofer, while other lines of those metals are seen: and an examination of the bright chromospheric lines shows that special rays highly characteristic of bodies which appear from other rays to be present in the chromosphere are absent, or are less frequent in their occurrence than others.

In the following tables the relation between our observations on reversals and Young's on the chromospheric lines is shown.

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In a subsequent communication we intend to examine carefully the contents of the preceding table. In the meantime we may remark that the group calcium, barium, and strontium, on the one hand, and sodium, lithium, magnesium, and hydrogen, on the other, seem to behave in a similar way in the chromosphere of the sun.

Presents, February 6, 1879.

Transactions. Freiburg im Breisgau :-Naturforschende Gesellschaft. Berichte über die Verhandlungen. Band VII. Heft 2. 8vo. 1878.

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The Author. Hall (Townshend M.) A Sketch of the Geology of Devonshire. roy. 8vo. Sheffield 1878.

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The Author. Moseley (H. N.) F.R.S. Notes by a Naturalist on the “Challenger,"

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