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Established
Current.

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“ The established current in the following experiments varied somewhat in the different experiments, but was constant during the same experiment; they cannot, therefore, be compared with each other without reference to the velocity of the established current.

Current in

Pipe. Saint-Martin's cone and cap,

227 233 25.5 2.08 Same cone without cap,

22.2 2.39 26.5 2.00 Cone, fig. 9, with its plate,

25.5 2.08 27.0 1.96 Same cone without its plate,

23.7 2.27 27.0 1.96 Model of a chimney ; 2 inches by the side ; end flat and horizontal ; 4 inches long,

26.02.04 18.7 2.83 Model of same dimensions ; top bevelled; angle of sides with horizon 40°,

26.0 2.04 21.5 2.47 Same; angle of plane of top inclined towards the blast, at an angle of 15°,

26.0 204 21.7 2.44 Same; same inclination ; .75 inch above top a plate 2.5 inch in diameter, .

26.0 2.04 21.7 2 44 Same, without the plate; inclined towards the blast 20°, 26.0 2.04 22.6 2 34 Same; inclined towards the blast 30°,

26.02.04 29.6 1 79 Same, at same inclination; plate 75 inch above the top, 26.0 2.04 25 6 207 Chimney model, with flat top inclined towards the blast, at the same angle, 30°,

26.0 2.04 52.5 1.00 Model and inclination same; plate 3 inches in diameter, .75 inch above the top,

26.0 2.0442.0 1.26 Conical revolving cap; angle of sides 470, apex towards the blast,

24.4 2 17|178 2.97 Conical cap, fig. 12,

27 5 1.92 18.5 2.86 Similar cone, with opening at apex, 1.25 inches in diam. eter, fig. 13, .

27.5 1.92|18.0 2.94 Conical revolving cap; angle of sides 47° : apex to blast, 27.2 1.94 21.2 2.50 Same, with opening at apex, 1.25 inches in diameter; apex to the blast,

27.2 | 1.9420.0 2.65

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66 The current established in the pipe was raised in temperature above that of the impinging current or blast, by placing the pipe in a vessel of hot water. The current in the pipe assumed a temperature of 104°, while that of the blast was 64o.

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“Elbow with a plate.87 inch from its mouth and turned towards the blast; temperature of current 64°; velocity 2.08 25.5 “ Same ; temperature of current 104°,

2.08 25.5 “ Several other experiments were made, but the results coincided so nearly that they may be considered as identical.

“ The proportions of those forms of ventilators which the Commit. tee have found most efficient will be placed in the hands of manufacturers."

Mr. Bond communicated the results of some recent observations on the planet Jupiter, and on the nebulæ Herschel Nos. 1357 and 1376 and the great nebula of Orion, as follows:

“ On the 28th of January and 3d of February, we had excellent opportunities for examining both hemispheres of the planet Jupiter, as on both occasions the atmosphere was in a remarkably tranquil state, and the definition good.

“On the 28th of January, at 10h. 30m. Camb. m. s. t., nine belts were counted, including those covering the polar regions of the planet. The principal equatorial belt was of an even surface, and its edges were nearly parallel. The next north was very irregular, particularly on its northern side. The other belts bore a striking resemblance to cirrus clouds, when about subsiding into the elongated form of cirrostratus. At the same time, the shadows of two of the satellites, the first and third, were seen transiting the disk. The preceding of these shadows when drawing near the limb became less intensely black, and was elongated in a direction nearly parallel to the axis of rotation of Jupiter. The third satellite was seen at the same time on the disk, as a black spot, and was then taken for the shadow of another satellite. It was not until we had compared its place with the ephemeris given in the Nautical Almanac, that we became satisfied that it could not have been a shadow. It agreed, however, with the computed position of the third satellite. Early in the evening, the first and third satellites were observed approaching the primary on the following side. The first appeared to be the smallest. The ingress of the third was observed, and when about half on the disk, it looked like a mountain projection on the limb of Jupiter. Neither of the satellites, when entirely on the disk, was visible at that time. Further observation was interrupted until about the time of ingress of the shadow of the third satellite, the first internal contact of which was noted at 6h. 41m. 51" sidereal time at the Observatory, the definition being at the time exceedingly fine. We now saw three black spots. The preceding was the shadow of the first satellite, which was now off the disk ; the next occupied the position of the third satellite; the last, near the following limb, was the shadow of the third satellite, very black, and larger than the satellite itself in the proportion of 5 to 3.

“On the 3d of February, at 9h. 30m. m. s. t., the opposite hemisphere was presented under equally favorable circumstances. Three belts

only were seen. The broad one, lying a little south of the equator, had no longer its sides parallel, as on the 28th of January, but a deep hollow on its southern edge, reaching nearly across on the preceding side. The principal northern belt was much broken and diversified with dark spots and inequalities. But the most remarkable feature was a curdling appearance of the whole intervals between the belts, and also of the entire region about the south pole.

“ On the morning of the 2d of February, we had a good view of nebulæ Herschel Nos. 1357 and 1376. Sir John Herschel's drawings, given in the Philosophical Transactions of 1833, are faithful representations of the wonderful phenomenon which they present. The great nebula in Andromeda shows a similar structure, but on a much larger scale. A fourth, which we find to possess the same peculiarity, is h 859, A. R. 114. 11"., Dec. +14° 30'; it resembles h 1357, but is fainter.

“ We find the great nebula of Orion to be connected with those about C and Orionis. Sir John Herschel's No. 75 in his Cape Catalogue of the stars in the nebula of Orion, which has heretofore been recorded as a single star of the eighteenth magnitude, is a double star. The direction of a line joining the components passes near '; the distance is estimated at two seconds. No. 91 of the same catalogue has been hitherto taken for a single star of the seventeenth magnitude. This likewise is double, and the direction towards of of the Trapezium, and the distance estimated at two seconds. The following one of this pair is as precisely as possible on the following edge of the bright part of the nebula, at the bottom of the Sinus Magnus."

A communication was read from Mr. G. P. Bond, respecting the great nebula in Andromeda ; the object of which was to direct the attention of astronomers to a remarkable peculiarity in its structure, which appears to have hitherto escaped notice. The paper was accompanied by a drawing, taken from repeated examination with the twenty-three-foot refractor of the Cambridge Observatory. Among the results of the employment of increased optical power upon this nebula has been the union with it of several neighbouring nebulæ, which have hitherto been regarded as distinct bodies. This paper was referred for detailed publication in the current volume of the Memoirs.

Three hundred and seventh Meeting.

April 4, 1848. — MONTHLY MEETING. The PRESIDENT in the chair. Mr. Bond communicated a farther notice respecting the third satellite of Jupiter, as follows: —

“In my communication of the 5th of February, I gave some account of a remarkable change which took place in the appearance of the third satellite of Jupiter, while transiting his disk on the evening of January 28th. I am now enabled, from subsequent observation, to confirm in a more detailed manner the account then given.

“During the evening of March 11th, this satellite was again seen as a black spot upon the disk of the primary ; but as several visitors were present at the Observatory, the observations were discontinued. It was remarked, however, that the spot was of less magnitude than the shadow which subsequently passed the disk.

“On the 18th of March, we were more fortunate. The state of the atmosphere proving favorable, I watched, with my son, the entire transit. The following are the results of our observations.

" At 8h. 15. sidereal time of the Observatory, we commenced, by estimating independently the relative order of brightness of the satellites ; it was, — first, third, second, fourth.

“ The third satellite, when close to the limb of Jupiter, suffered no diminution of its brightness or apparent magnitude.

“At the first contact with the primary, the latter seemed to recede from the satellite.

“At 8h. 51", the contact of the centre of the satellite with the limb of Jupiter took place.

“gh. 55". First internal contact; the satellite was then seen distinctly on the disk, brighter than Jupiter, although it had entered on a bright channel between the great belt and a smaller one south of it. The satellite was thought to be less bright on its southern limb.

" At 9h. 15m., it had decreased in brightness so as to become hardly perceptible.

“ At 9h. 18m. 15“, my son, who was now observing, exclaimed quickly, — The dark spot is coming on; I now see the satellite ; the dark spot is on the right hand, perhaps a little above !' On examination, I found the spot was quite distinct.

m.

“gh. 21". The dark spot increases, and is now seen on the satellite. “ 9" 33". The spot has become conspicuous.

“ At gh. 40m., the diameter of it was measured with the spider-line micrometer, in the direction of the belts of Jupiter, and was found to be 0."50 by B,, immediately after the angle of position of what was considered to be the longer axis = 170°. “The following diameters were then measured in the first position :

h.
At 9 44

6 Bi 66 Bz. 6 Bi.

0.71

by B, 9 47

0.85 9 55

1.10 10 00

1.00 10 02

0.99 “ 10h. 5o. It appears perfectly black and nearly round; tried different powers; it is best seen with 400 ; there are doubts of the spot being round, but could not decide on any other form.

“ 104. 32m. B, thinks it is not so black as it was.

“ 10h. 35". Satellite past the middle, and keeps in the bright channel.

“ 116.7m. The satellite now appears black; it has accomplished three quarters of its journey across the disk.

“116. 17m. Spot dark as ever, perhaps darker. B, thinks it in. clines to the south-following limb of the satellite.

"11". 37". The satellite is seen broad, but not so dark; it is getting near the edge.

“ 116. 52".. Can just discern the spot, but the altitude is getting low; however, the seeing is remarkably good, at times, for so low an altitude. It is now doubtful whether the bright part of the satellite can be seen or not.

“ 11" 58". Neither spot nor satellite is visible, absolutely.

“ 124. 6m. One half the satellite is seen as it passes off the disk; it is bright.

“ 126. 12m. The last external contact was observed by Bz, who noticed that the limb of Jupiter appeared flattened.

“ 12h. 21m. The third satellite is now seen at a considerable distance from Jupiter, and the order of brightness is, - first, second, third. The fourth satellite is under eclipse.

" It is evident that the third satellite is not now one half the brightness of the second, which it far surpassed before the transit took place.

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