Comparison of the Yearly Variation. First 12 months obsery. Second 12 months observ. Morning. April 24° 09' 18' 24° 21' 12 24° 15' 25" 24° 12 5324° 23' 5324° 15' 3011 24 14 08 24 21 45 24 16 20 24 20 37 124 17 39 24 20 30 24 18 02 24 20 36 24 15 05 24 19 03 24 16 46 24 20 12 24 15 11 24 21 51 March.... Mean 24 14 36 24 2142 24 15 41 24 14 42 24 22 22 24 16 28 24 14 36 24 21 42 24 15 41 (To Dr. Thomson.) MY DEAR SIR, Hackney Wick, April 17, 1815. I have the pleasure to send you the conclusion of the second year's observations on the variation of the magnetic needle. The number of observations made in the first year, and set down in the Annals of Philosophy, were, in the morning 294, at noon 265, and in the evening 141. But it is to be remarked that the numbers set down are the means of the observations made with two needles, and each consisting of 14 readings off on the arc of the instrument. If, therefore, the former numbers be multiplied by 28, the total amount will be 19600, and the number in the second twelve months will be found 22764. As every attention was paid in making the observations, and the two needles rarely differed three minutes, seldom two, it may be presumed that the variation is truly determined, and has not yet arrived at its maximum, the annual increase being 31". It certainly would be a desirable circumstance if observations were made, at this period, in different parts of the world, especially in those places where the variation is great ; and as I perceive in Number xxv. of the Annals of Philosophy, that Mr. Scoresby, jun. of Whitby, has kept meteorological journals during his voyages to Davis's Straits in the years 1813 and 1814, perhaps he, or some other Gentleman, may favour your readers with observations on the variation of the compass in that part of the world. That a comparison may be made of the present variation with that in the year 1790, I have inserted Capt. Brown's observations, on whose accuracy dependance may be placed. His journals are in my possession. He commanded the ship Butterworth ; and was furnished with an accurate azimuth compass, made by Mr. Dolland for the purpose of making the observations now inserted. I am not acquainted with the alteration in the variation which has taken place on the Continent. From several observations I made in the year 1787, at La Rochette, near Neuchatel, in Switzerland, the variation was 19° 7' 14" W. The latitude of this place, from many observations, is 47° 00' 15" N.; and the longitude, deduced during my residence there from solar eclipses and occultations of the stars by the moon, 28' 40" E. in time, or 7° 10'00' in space, of Greenwich, Not being aware that any observations have been made to determine the situation of the supposed highest mountain in Europe, I take the liberty of sending you the latitude of Monte Blanc, from an observation I made under very favourable circumstances, on its summit, in the month of August, 1787 ; the- latitude, deduced from the meridional altitude of the sun, is 45° 49' 59'' N.; and as the summit bears from Neuchatel by the compass S. 20° 54' 09" W. by using the difference of latitude and the true bearing, the longitude in space is 3' 10" W. of Neuchatel, and consequently 7° 650% E. from Greenwich. The lake of Neuchatel I found to be 1428 feet above the English Channel. I remain, my dear Sir, yours very sincerely, MARK BEAUFOY. ARTICLE X. Observations on the Uses of the Dorsal Vessel, or on the Influence which the Heart exercises in the Organization of articulated Animals, and on the Changes which that Organization experiences when the Heart or the Organ of Circulation ceases to exist. By M. Marcel de Serres. (Continued from p. 199.) This last series of researches being finished, it remained to determine the cause of the contractions and dilatations of the dorsal yeşsel, and of what importance that vessel was to the general economy of insects. These contractions and dilatations might depend . on various causes, or only upon the peculiar structure of that organ; though it was difficult to adopt such an opinion, because the absence of vascular vessels announced that the humour contained in it did not circulate. To determine the point I began by examining what influence the muscles which surround the dorsal vessel might have upon its contractions. The mole cricket, being a very lively insect, was chiefly employed by me in these researches. The dorsal vessel being brought in view, I removed the abdominal muscles (and the adipose membranes of necessity) in the middle part of the abdomen, while I left the dorsal muscles quite entire in the upper and lower part of the abdomen. This being done, I remarked that the dorsal vessel always contracted in those parts where the muscles had not been removed, and these contractions were the less lively the nearer they came to the muscles that had been removed. However, by degrees, some contractions took place in the parts of the dorsal vessel from which the muscles had been removed; but they were 'always weak, and seemed to proceed from portions in which the muscles still existed. In other cases I removed entirely the dorsal muscles; then the contractions of the dorsal vessel became weaker by degrees, and ceased at last, though after a very considerable interval. Dr. Encontre* was so good, at my request, as to repeat these experiments. He observed that, after removing the dorsal muscles, the contractions of the dorsal vessel diminished, by degrees in the rings from which these muscles had been removed ; while they continued still strong in those rings where the muscles still remained. In a ring in which he had left only some traces of muscle, the dorsal vessel still continued to contract, when its contractions bad ceased in all the parts from which the muscles had been removed, I must remark, that the insects subjected to these experiments are not dead, when all the dorsal vessels have been removed ;. but what is still * He is the son of M. Daniel Encontre, known with eclat as a mathematician, Vol. V, No V.'' 2 A a more singular, they continue to live after the dorsal vessel has been entirely removed. I have seen the caterpillar of a sphinx atropos breathe for six hours after I had removed the dorsal vessel. The inspirations and expirations still continued, and air bubbles broke from the ends of the trachexe which had been cut at the removal of the dorsal vessel. If this organ were a heart, how could insects, possibly live so long after being deprived of it. To be convinced of the difference, let the heart be removed from those animals in which it exists even in the least complicated state. Not one will resist its loss, most of them will be dead before the removal can be completed.. I must observe, that after the removal of the dorsal vessel, insects are no longer able to move about; but life notwithstanding still continues. This intensity of life is found in all animals that have no centre of action : other animals die very speedily. One would think theré ought not to be a great difference in this respect between the farcheurs and spiders, or between the scolopendras and scorpions, and yet there is a very great one. The scorpions and spiders die almost immediately after exposing their heart; while insects live often six or seven hours after removing the organs most essential to life. Yet both have a nervous system composed of a series of ganglions; but the insects have no centre of circulation, or, which is the same thing, they have no heart. We have seen the influence of the dorsal muscles on the contractions of the dorsal vessel. As this influence might not be the only one, I endeavoured to determine those which might belong to the tracheæ and nerves. Before engaging in this new set of experiments, I wished to determine whether by means of metallic exciters I could render the contractions of the dorsal vessel more frequent and stronger. When the two exciters were brought into contact the insect exhibited symptoms of pain; but the dorsal vessel, instead of increasing in liveliness, beat always more and more slowly. On continuing the contact of the wires of zinc and copper between the membranes of the dorsal vessel, the humour contained in this vessel gradually coagulated, and the contractions ceased by degrees. Thus the galvanic agent in the present case produces effects similar to the chemical, with this difference, that it acts less rapidly. It might be concluded, à priori, that the trachexe have a considerable influence on the contractions of the dorsal vessel, on account of the great number of them which enter it and constitute one of its coats, and on account of the great influence of air on the organs of insects. . But But great difficulties prevent us from determining that influence; the most insurmountable of which is the impossibility of separating the trachee from the dorsal vessel : for, without such a separation, we cannot judge of the influence which they exert on its contractions. I have not been able to surmount these difficulties in thiose insects which have tributary traches, So that I can only depend upon one experiment, which succeeded : very well on a caleoptera lamellicornis. I removed with all possible care, in the ateuckus semi-punctatus, the vesicular trachea which surround the dorsal vessel, as well as their ramifications. When they were removed the contractions of the vessel diminished by degrees. I had indeed removed some inuscular fibres; but in 60 small a quantity, that I do not believe that cause had a remarkable influence. These contractions have continually gone on diminishing, and the diminution was much greater than what is the consequence of pain, and of the cessation of certain functions. I believe, therefore, that the contractions of the dorsal vessel are proportional to the quantity of adipose tissue; the energy of the : muscular fibres that surround it, and of the number of tracheæ which enter into it, or of the air which it receives. Let us see now whether the nerves have not some influence on these contractions, as the dorsal vessel receives a certain number of them. To determine this influence, I removed the spinal marrow with the nerves coming from it, as far as I could distinguish them, and then examining the contractions of the dorsal vessel, I could not perceive that they were sensibly enfeebled. I repeated this. experiment on a great number of individuals of different orders, and I always obtained the same result. Hence I conclude, that the nerves have no very sensible influence on the contractions of the dorsal vessel. It is possible, that in all these animals in which the nervous system is very much divided, and the principal centre has little preponderance, the nervous influence is less distinct. This I shall endeavour to determine by future researches. It remained still to determine whether the contraction of the dorsal vessel does not depend in part on the circulation of the liquid which it contains. We have already observed, and the observation, since the time of Malpighi has been renewed by all anatomists, that the humour of the dorsal vessel has a very irregular motion, and that the fluid often appears to go from the head towards the tail, and at other times to take a contrary direction. Sometimes the dorsal vessel contracts at its two extremities, while these contractions do not take place in the middle of the organ, especially if the dorsal muscles have been removed in this part. So that the liquid in the dorsal vessel appears at one time to move with extreme rapidity, at another very slowly, without any apparent connexion between this irregularity and the state of the insect. But how can this irregular motion be reconciled with the circulation of a fluid analogous to the blood, and how can a circulation take place without vessels? All these facts are in themselves so conclusive, that it is difficult to consider the dorsal vessel as a heart, and, of course, to admit that the contractions are produced by a liquid in circulation. In the second place, if we pierce the heart of any animal whatever, the moment the blood arrives it rushes out in a quantity proportional to that which enters the heart. It was important, therefore, to determine whether this would happen when the dorsal vessel of insects is punctured. For that purpose I chose' 1: A this achez |