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envelopes it. Thus the strong outer covering of the seed is produced below into a very sharp rigid spine ; and terminated above by a long awn, which is articulated to its summit. Originating near the base, and proceeding up certain ridges on this the investing valve chiefly, are lines of stiff hairs pointing upwards. The awn, when fully developed, is about thirty times the length of the seed, or about fourteen inches. It is round, tapering and plumose, with the exception of about three inches at the base, wbich are compressed, longitudinally sulcated, and without hairs.

The seed, therefore, and its appendages, possess a structure such as is imitated in a barbed and feathered arrow, which is so well calculated to find its way into the ground in a vertical direction. Many seeds, however, possess a similar structure, and it is not this which gives to the awn of the stipa its most striking peculiarity. It is a change which takes place upon the awn, after it has left the plant that produced it. When it has fallen from the parent plant, it enters the soil vertically, and in a few hours the base and sulcated part of the awn becomes twisted, and the feathered portion becomes horizontal. In consequence of which, it is blown round by the autumn winds like a vane, and every turn screws it farther down into the earth ; for the hollows and ridges which, when it remained upon the plant, were only longitudinal sulci, have now given rise to the hollows and elevations, in a word, to the threads of a screw. Thus it is moved down, and whatever is gained, is prevented from being undone by a reverse motion of the vane, in consequence of the stiff hairs upon the glume which act as barbs.

When it has been thus worked down into the moist soil, into the situation most favourable for germinating, the attachment between the awn and seed is dissolved; for having drawn up many when they were in this condition, I have invariably procured the awn only, and never, by any chance, the seed. Such appears to be the function of the “ spiral articulated deciduous awn of this interesting species *

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* The seeds of the Stipæ often occasion great inconvenience and trouble to travellers, and even to the domestic cattle of the districts where they grow. This fact is well stated in the following notice by Mr Raspail.Ed.

« On the morbid accidents to which animals are exposed by the seeds of Stipa pennata and capillata. It is known that the husks, genus Stipa terminate at the base in a reversed cone, which is very sharp, and covered with stiff hairs directed upwards, so that when the point penetrates into any substance, the hairs not only prevent it from coming out, but contribute to make it go deeper. M. Desfontaines, in his Flora Atlantica, and M. Lamarck in the Ency. clopedie, have pointed out the inconveniences to which a seed so organised subjects travellers passing over the fields of Barbary, Greece, and Portugal, at the time of ripening of the stipas, The seed penetrates into their clothes, and sooner or latter disconveniences them in a high degree, by producing scratches of various depths upon the skin. A great mortality of the cattle, which took place in 1823, in the neighbourhood of the village of Berczel in Hungary, afforded an opportunity to the Professors of the Royal University of Pesth, of making known'a still more singular effect produced by these seeds. It was found that the seeds of the stipas, which abound in the pasture grounds of Berczel, stuck to the wool of the sheep, penetrated into the skin, and even made their way to the internal organs. On dissecting a great number of these sheep, seeds were found in the vicinity of the liver and in the peritonæum, and the skinu-xamined between the eye and the light, had the appearance of s uave alread. As these grasses occur in all the south

The accompanying drawing represents the seed and its appendages, more or less magnified.

Explanation of the Figures in Plate I. Fig. 6. The two valves of the glumaceous perianth, with the stiff hairs,

the spine and articulated awn. 7. The grain, with part of the skin torn at the base, to shew the

albumen, of which nearly the whole is composed, the cotyledon

and the embryo.
8. The seed, with a fourth part of the awn, to shew its form when

ready to separate from the spike.
9. The same, as it appears some hours after separation.

Account of the Observations and Experiments made on the

Diurnal Variation and Intensity of the Magnetic Needle, by Captain Parry, Lieutenant Foster, and Lieutenant Ross, in Captain Parry's Third Voyage, with Remarks and Illustrations. By PETER BARLOW, F. R. S. Mem. of the Imperial Academy of St Petersburgh, &c. (With a Plate.) Com

municated by the Author. As the experiments referred to in the head of this article were performed under such extraordinary advantages of locality, of instruments, and of observers, they cannot fail to be highly interesting to every one who has paid attention to this curious and important branch of natural philosophy. With regard to locality, no place could have been more admirably situated than Port Bowen, in latitude 73° 14' N., longitude 88° 54' W., with a dip of 88° 1', and consequently within a very short distance of the magnetic pole, and yet sufficiently remote to leave to the needles a natural directive power, which they would in all

of Decem

probability have lost, had the approximation to the Pole been much greater. With regard to instruments, every thing that could be effected by the skill of the most distinguished artists in London, was liberally supplied to the expedition by the Government; and as observers, it is sufficient to mention only the names of Parry and Foster, as they cannot fail to inspire us with every possible confidence, both with respect to the accuracy of the observations, and to the most careful and unbiassed registry of the results. It is but fair, however, to state, that these two distinguished individuals alone, would not have been able, with all the zeal they are known to possess, to have obtained such a series of results as those to which we are now referring. It was necessary for this that they should be seconded by the cordial assistance and co-operation of the other officers of the expedition. This assistance was cheerfully given ; and it is acknowledged in the most handsome and liberal terms by the authors of the memoir in which these experiments are recorded, and which has been recently published as a separate part of the Transactions of the Royal Society for 1826.

The experiments commenced about the 10th of December 1824, and were continued to the end of May 1825; and, when we consider that, for a considerable part of this time, the sun was below the horizon,—that the thermometer was sometimes 40° below zero,--that the place of observation, a snow house,

ern parts of Europe, the above fact ought to fix the attention of the agriculturists of those countries. The stipæ do not furnish good fodder, and the meadows would lose nothing by their absence. If they could not be extirpated all at once, the flowers are surmounted by an awn upwards of a foot long, by which they might easily be plucked off, before detaching themselves spontaneously. Should a seed happen to have buried itself in the substance of the skin, it would require to be extracted wmtcho ordinary means, for accidents of this kind are not to be remedied by a m

treatment."

mbe husks

1

was at a distance from the ships, in order that the needles should be out of the influence of the iron on board ; and that, notwithstanding these obstacles, the needles were carefully watched, the experiments performed, and the results carefully registered every hour, and frequently oftener, during this whole period; we shall feel convinced, that more than common exertions were made, and more than usual interest must have been excited, in the pursuit of these curious and valuable experiments ; and, if we add to this, that these energies and these means were employed in a situation where Nature has placed her great depot of magnetic powers, and where every phenomenon of this kind is exhibited on the grandest scale, we shall then, and not till then, sufficiently appreciate the value of these interesting and important results.

With this feeling, I have thought that a brief abstract of these experiments would be acceptable to many of the readers of the Edinburgh Journal, particularly to those who have not the opportunity of consulting the original memoir; and I have accordingly, in the following pages, endeavoured to convey within the least compass, a general view of the subject, and have ventured also upon one or two illustrations of some of the theoretical points touched upon by the authors of the papers in question.

The first of the magnetic articles is by Lieutenant Foster, from which it appears, that, previous to his leaving England, he had determined upon making a series of observations on the daily variation of the magnetic needle, when any opportunity offered of so doing; and the first occurred at Whale Fish Islands, during the time of trans-shipping the stores from the transport which had accompanied the expedition to that place. The time employed in these experiments was only three days, consequently the results are not so certain as we could wish ; but it is satisfactory to find, that the few facts which were obtained agree remarkably well with each other, both as to quantity and to the time of the day when the variation was the greatest westerly,—the least westerly variation, or the maximum of easterly variation, occurred during the night, and w observed. The greatest daily variation westerly was 23', occurred at 1h 10' P. M., at which time the sun was west by the mean variation being 70° 2' W., and dip 82° 53' W. portant remark, distinguished above by italics, seems to hav strong incitement to Lieutenant Foster to prosecute again on a larger scale the next favourable opportunity not occur till the ships were laid up for the winter at At this place, as we have already stated, the experim gun on the 10th of December 1824, on one needle

.

course of this month, however, the varied phenomena which this one exhibited, while every thing besides appeared to partake of the stillness and monotony of this dreary region where it was posited, excited that degree of interest amongst the officers of the expedition which we have endeavoured to describe ; and with the new year commenced a much more extended series of experiments on the daily variation, the variation of intensity, and, in fact, of the whole series of which it is intended to give a general outline in the subsequent pages.

The detail of the daily variation experiments forms the second of these articles. After describing the needles employed, marked No. 1, and 2., and a third, employed exclusively for determining the changes of intensity; and also acknowledging the assistance of Lieutenants Sherer, Ross, Messrs Crozier, Richards, and Head, as also that of Mr Hooper for the delineation of a very accurate diagramo, offering a graphical exhibition of the several changes; the authors proceed to take a sort of general review of their results, as follows:

“ Soon after the observations were commenced, it was ascertained that, twice in every four and twenty hours, the needles moved past a certain point, which may be denominated the zero, or mean magnetic meridian ; a fact which was first rendered clearly apparent from the accompanying diagrams, already mentioned, by which it appears, that, in every instance except one, both needles every day passed the line in question. On a single day, February 24., the needle No. 2. did not arrive at it during its eastern motion.

The means of the times of the needle passing this zero, as deduced from four months' continued observations, is 6 hours 15 minutes A, M., and 4 hours 37 minutes P, M., the mean time in each month being as follows:

1825, January,

6 hours 00 min. 4 hours 00 min.
February,

6
30

4

00
March,
5 30

5
April,

17
00

5

30

A, M.

P. M.

00

15

4

37 To avoid the insertion of many useless figures in the tables, the resulting amount of easterly or westerly deflection on each side of the zero has been computed.

The maximum westerly variation at Port Bowen, appears from these observations generally to have occurred between the hours of 10h A. M. and jm P. M., the mean result of 120 days' observations being 11h 49m A. M. The minimum westerly variation, or the greatest deflection of the north end of the needle to the eastward, took place between gh P. M. and 2h A. M., the mean time deduced as above being 10h 1m P. M.

* In order to give an idea of this diagram, we have given a sketch of it in Plate V., for six days, viz. from the 20th to the 26th of March,

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