Chapter XXVIII: Appendix: D

THE AURORA AND OZONE.

[Sidenote: Aurora and ozone. Dr. Allnatt’s notes and conclusions deduced therefrom.]

While Part I. was in the press, Dr. Allnatt, formerly of Frant, and for many years the well-known meteorological contributor to ‘The Times’ newspaper, kindly placed at my disposal his large series of notes. Upon an examination of these we came to the following conclusions:—

1. That Auroral periods are also periods of comparative abundance of ozone.

2. That instances are by no means wanting in which an abnormal development of ozone appears to be coincident with the manifestation of an Aurora.

[Sidenote: Year 1870 remarkable for sun-spots, auroræ, and ozone.]

In reference to the first point, it is found, as the result of an examination of Dr. Allnatt’s notes, that particular years and months are notable at once for Auroræ and for ozone in abundance. 1870 was one of these years, and was specially recorded by Dr. Allnatt, in his ‘Summary for the Year,’ as remarkable for sun-spots, Auroræ, and ozone.

[Sidenote: Particulars of some of the monthly records.]

The month of February in that year was marked by intense cold and brilliant Auroræ. Atmospheric electricity was feeble, but ozone was, throughout the month, well developed; and there was no tangible period of antozone.

In the month of April of the same year, eight days consecutively (19th to 26th) were marked for ozone 10, the maximum of Dr. Allnatt’s scale.

In May of the same year there were magnificent Auroræ, and atmospheric electricity was intense. Ozone was scanty; but this was accounted for by the wind being generally E.N.E., ozone being mostly developed with a W. or S.W. wind, and a moist state of the atmosphere.

In August 1870 the unusually large number of 22 days were recorded for a maximum of ozone.

September 1870 was hardly less remarkable, with 19 days of maximum. It was recorded that there were splendid Auroræ during this month, and the solar spots were very large.

October 1870 had 20 days of maximum ozone, and November had several fine Auroræ and maxima of ozone noted. In fact, nearly every month in that year was referred to by Dr. Allnatt for displays of Aurora (of both Arctic and Antarctic forms) and for a development of ozone very considerably above the average.

[Sidenote: Year 1871.]

The year 1871 had more or less of the same character. In the month of October of that year, fine Auroræ were prevalent, and ozone was registered as at its maximum during 22 days.

There seems reason to conclude that if a systematic comparison of annual or other periods of Aurora and ozone development were made, it would result in disclosing a connexion (probably an intimate one) between the two phenomena.

[Sidenote: Instances showing a connexion between a specific Aurora and an ozone maximum.]

With reference to the second point, the following (among other) instances may be quoted, for the purpose of showing a connexion between a specific Aurora and an ozone maximum.

The Aurora of 24th September, 1870, was splendid and universal, being seen in Europe, Asia, Africa, America, and Australia. Ozone reached, on the morning of the 24th, 8 of the scale (the scale running from 1 to 10), and, on the morning of the 25th, 10, the maximum.

In October 1870 there were grand displays on the 14th, 20th, 22nd, 24th, and 25th, and ozone was correspondingly abundant, as is seen by the following Table:—

+-------------------+----------+------+------------------------+
| Date. | Aurora. |Ozone.| |
+-------------------+----------+------+------------------------+
|1870, October 14th.|Aurora. | 8 |The display of the 24th |
| ” ” 20th.|Aurora. | 10 | was accompanied by |
| ” ” 21st.|None seen.| 5 | the formation of a |
| ” ” 22nd.|Aurora. | 10 | corona, and that of |
| ” ” 23rd.|None seen.| 8 | the 25th was splendidly|
| ” ” 24th.|Aurora. | 10 | seen in Edinburgh. |
| ” ” 25th.|Aurora. | 8 | |
+-------------------+----------+------+------------------------+

The foregoing figures somewhat point to the conclusion that ozone quantity rises and falls coincidently with the Aurora displays.

The following seems, however, a case still more strongly in point.

+-------------------+-------+---------------------+------+
| Date. | Wind. | Aurora. |Ozone.|
+-------------------+-------+---------------------+------+
|1871, January 25th.| E.S.E.| None seen. | 0 |
| ” ” 26th.| N.N.W.| None seen. | 2 |
| ” ” 27th.| E.S.E.| Aurora at night in | |
| | | N. and S. horizons.| 10 |
| ” ” 28th.| E. | None seen. | 8 |
| ” ” 29th.| S.E. | None seen. | 2 |
+-------------------+-------+---------------------+------+

It is curious, in examining the above Table, to note how the ozone rose, notwithstanding an east wind, from 0 on the 25th, and 2 on the 26th, to 10 on the 27th, when the Aurora appeared, and 8 on the 28th, when it might have lingered; and how it again descended to 2 on the 29th.

The case of the Aurora of 6th of October, 1869, when a broad belt of Aurora was in the north, is also an illustrative one, as will be seen by the following data:—

+------------------+------+------+-------+
| Date. |Wind. |Ozone.|Aurora.|
+------------------+------+------+-------+
|1869, October 5th.|S.S.W.| 1 | — |
| ” ” 6th.|S.S.E.| 5 |Aurora.|
| ” ” 7th.|S.S.W.| 10 | — |
| ” ” 8th.| S. | 10 | — |
| ” ” 9th.| S.E. | 5 | — |
+------------------+------+------+-------+

The Aurora of the night of the 6th was here represented by the ozone-paper of the morning of the 7th with a maximum of 10, which lasted till the 8th.

[It should be borne in mind, in examining these Tables, that the Aurora is of the night of the given date, while the ozone-papers are taken and recorded in the morning of the date quoted.]

[Sidenote: Other instances.]

We will now take instances where the ozone has not reached its maximum; but even in these cases a certain amount of rise and fall of the ozone development towards and from the Aurora is traceable.

+-------------------+--------+------+-------------------------+
| Date. | Wind. |Ozone.| Aurora. |
+-------------------+--------+------+-------------------------+
|1871, April 8th| S.S.E. | 5 |Aurora on 9th, but |
| ” ” 9th| S.S.E. | 8 | wind E. and unfavourable|
| ” ” 10th| S.E. | 5 | to ozone. |
+-------------------+--------+------+-------------------------+
|1871, November 9th| N. | 5 |Aurora on all three |
| ” ” 10th| N.W. | 8 | nights. |
| ” ” 11th| N. | 5 | |
+-------------------+--------+------+-------------------------+
|1872, February 3rd| S.W. | 4 |Aurora on night of the |
| ” ” 4th| S.S.W. | 5 | 4th represented by |
| ” ” 5th| S.W. | 8 | ozone-paper of morning |
| ” ” 6th| S.W. | 5 | of the 5th. |
+-------------------+--------+------+-------------------------+

Other cases are, we are bound to say, found, in which ozone was either not remarkable for quantity, or positively fell during the Aurora, as, for instance, this:—

+-----------------+------+------+------------------------------+
| Date. | Wind.|Ozone.| Aurora. |
+-----------------+------+------+------------------------------+
|1874, March 16th |W.N.W.| 6 |Aurora on the 18th represented|
| ” ” 17th | S.W. | 6 | by test-paper of |
| ” ” 18th | W. | 5 | the 19th with only two |
| ” ” 19th |S.S.W.| 2 | degrees of discoloration. |
+-----------------+------+------+------------------------------+

It is, however, possible that such instances may be accounted for, either by some reaction on the test-papers after they have been coloured, or by some accidental antagonistic circumstance affecting the tests. The following is a case well illustrating this:—

+------------------+------+------+---------------------------------+
| Date. | Wind.|Ozone.| Aurora. |
+------------------+------+------+---------------------------------+
|1874, January 31st|N.N.W.| 6 |There was an Aurora on |
| ” February 1st| N.W. | 8 | the night of the 2nd represented|
| ” ” 2nd| N.W. | 2 | by the ozone-paper |
| ” ” 3rd|N.N.W.| 4 | (4 only) on the |
| ” ” 4th|E.N.E.| 8 | morning of the 3rd. |
+------------------+------+------+---------------------------------+

This instance would seem strongly opposed to the theory of a connexion between Aurora and ozone but for the fact that on the 2nd, when the Aurora was seen at night, and on other days in the same month, Dr. Allnatt has recorded a strong wave of antozone to have swept over the whole of England, and blanched the ozone-papers, however deep their coloration might have previously been. Indeed, it is easy to understand that some antozonic influence may, at times, disturb the evidence of the test-papers, even in so elevated and apparently pure an atmosphere as that of Frant.

It may not be considered that the foregoing instances are enough to establish a case of ozone=Aurora; but there seems, at least, sufficient to base a requisition for further inquiry upon.

It would, too, be interesting to investigate whether Auroræ and ozone development are respectively localized. Mr. Ingall’s fine Aurora, seen at Champion Hill, S.E., July 18th, 1874 (_antè_, pp. 22 and 23), was not observed at Frant, and the ozonoscopes there were described as blanched by antozone.