= = difference 0,23 the amount of deviation in arc, showing that the west end of the axis is higher by that quantity than the east end, since the mean of the western readings is greater than the mean of the eastern. This quantity, divided by 15, will give the proper factor for inclination. It is more convenient that the scale should be divided into units, each of which is 15". 66 Having in this manner determined the inclination of the axis by the level, the correction to be applied to the time of observation of any star made during the existence of that error, may be computed from the following formula: b= the factor for inclination of the axis + if the west end be too high. the polar distance of the star. λ the co-latitude of the place. “This formula in words gives the following practical rule. To the log. of the factor for inclination of the axis, add the log. co-secant of the polar distance, and the log. co-sine of the difference between the polar distance and the co-latitude: the sum 20 will be the log. of the correction in time required. Convinced as we are that a third edition will soon be called for, we would suggest the following additions to the author's consideration. A general preliminary essay on the causes of derangement in astronomical instruments, and the nature of the adjustments which are hence rendered necessary, whenever the instrument is used. These causes of derangement are principally the unavoidable imperfection of workmanship, the wear of the centres by friction, and the effects of temperature and gravitation in altering the form of the divided limbs of graduated arcs. We think some details of the method of observing and noting the times, would be both useful and interesting-thus, the observer having written down the integral minute when he takes his place at the telescope then counts the seconds'-beat, of his clock, and notes them at the passage of the star over each wire of the micrometer. The technical mode of "reading off" the micrometers, when several are attached to the same circle, also seems to demand some description. A less concise notice of the method of obtaining the longitude by the eclipses of Jupiter's satellites, in p. 102, is very desirable, from its importance; it is at present far too slightly touched on. There are one or two instruments not noticed which would seem to require description in such a work, and some are, perhaps, too briefly alluded to; Captain Kater's collimator, and the repeating-table, p. 19, may be cited as instances of the two cases alluded to. A glossary of the technical and scientific terms made use of would be a useful addition; thus, for example, in p. 29, the term "sprung at its aperture," would not be intelligible to one less conversant than ourselves with instruments; and the term collimation, might be dwelt on more at large, considering its importance and frequent recurrence. We make these suggestions from a conviction that they are desiderata, and that few persons could treat them better than our author; otherwise, where so much has been done so well, it might seem invidious to introduce even these hints. One omission we feel we ought to supply, as it happens to be in our power. We do it the more readily, because the improvement in question having been attributed to, if not claimed by, another, it becomes. an act of justice to assign it to the inventor. In page 57, is mentioned "an excellent contrivance for taking altitudes and depressions with the box-sextant," which was shown to the author by a professional gentleman. This gentleman, we believe, was Mr. Macneill, the civil-engineer; we are sure that he was the inventor of this modification of the instrument. Subsequent experience has decided that the new power is a very useful Several practical civil-engineers of eminence have so expressed themselves with regard to it, and now consider a box-sextant so provided as the most convenient instrument that can be taken, when an accurate comp-d'œil is to be made of a new line of country. It has been found that one of the two spirit-levels mentioned in the text, may be dispensed with, and that even when this is done, a very little practice enables an observer to take an angle of altitude within 5 sec. of the truth *. In the paragraph of the work describing this addition to the box-sextant, for "plane-sight" read “plain-sight." MISCELLANEOUS INTELLIGENCE. Precision in Scientific Terms. CONDUCTION-CONVECTION.-"The transfer of heat by communication may be distinguished into transfer by conduction, and transfer by convection. The former being applied to the method of transfer which takes place in solid bodies, and the latter in fluids. When a solid mass is placed in contact with a hot substance, the heat is communicated from one to the other, and is transmitted through the solid, being conducted from one particle to another, with a velocity which depends on the nature of the substance in contact; hence substances have been divided into good and bad conductors. But when heat passes by communication from a hot body into fluids, the transfer takes place in a very different manner. The particles of a fluid, becoming heated, expand, and then being specifically lighter than those particles of the surrounding fluid which have not received an increase of temperature, they ascend, and fresh particles descend into their places; and the transfer of heat by this motion is so rapid, that if one thermometer be placed at the top and another at the bottom of a vessel of fluid which is heated from below, the upper thermometer will begin to rise almost as soon as the lower: this, then, is the transfer by convection. The conducting power of fluids is extremely small. For if heat be applied to the upper surface of a fluid, the convecting motion of the particles cannot take place, and consequently, the only transfer of heat which can take place, will be by conduction, in consequence of the contact which subsists between the particles; and the transfer which takes place this way is so small, that Count Rumford denied that water could conduct at all. But it appears that all fluids conduct heat in a slight degree. Hence the transfer by communication, that is, by conduction and convection, depends upon the nature of the substance. The term convection, which was much wanted, is introduced on the authority of Dr. Prout, Bridgewater Treatise on Meteorology, &c."-Webster, Principles of Hydrostatics, 1835. CLIVITY-ACCLIVITY-DECLIVITY.— I have rendered the word pente by slope, in preference to inclination, inclined plane, or gradient, considering the two former, though generally used, as improper expressions, and the latter, to say the least of it, as having so very little to recommend it, that I hope it will have an extremely short existence in our nomenclature. Judicious and appropriate terms are of the greatest importance in speaking and writing on scientific subjects, particularly when technical expressions must of necessity be introduced. "It is highly desirable to keep scientific knowledge precise, and always to use the same terms in the same sense*." A gentleman of high literary acquirements, to whom I applied, and who has taken the trouble to consider the subject, has suggested the term clivity, as one that is of more legitimate etymology than gradient, and more appropriate than either slope, inclined plane, or inclination. I regret that I was not in possession of this term before I commenced the translation; the words * Lord Brougham's Discourse on Natural Theology. acclivity, declivity, which may be so regularly derived from it, would have enabled me to have given the sense of the original with greater perspicuity."— Macneill, Translation of Navier on Railways, 1836. Remarkable Depression of the Barometer. THE barometer at the Royal Observatory, Greenwich, at noon on the 28th ult. stood at 28.525 in. A depression which has not been observed at this season for more than thirty years. The day was rainy, and there was some wind at night: nothing more remarkable was observed. Professor Daniell gives the following as the barometrical points of March in London : The depression on the 28th ult. was therefore lower than the least height here given, by 0.345 in. Recent Hypothesis on the Formation of Rain not new. IN your Magazine of Popular Science for February, p. 23, there is an hypothesis stated to be given by Professor Phillips, of King's College, in explanation of the difference in the relative quantities of rain collected at different heights. Professor Bache of Pennsylvania, in a letter communicated to the Franklin Institute Journal, dated Dec. 1835, observes :-" In investigating a complex subject of this kind, the experimenter not unfrequently proceeds as if it were entirely new, and to this cause I attribute the fact, that Professor Phillips was not aware that he had been anticipated in his hypothesis. The fact that a less quantity of rain is received by a rain-gauge upon an elevation than upon the subjacent ground, was proved about the year 1766, by the experiments of Dr. Heberden, Lord Cavendish, and others*. The hypothesis now advanced by Professor Phillips, was suggested about 1771, as an explanation of their curious results by Dr. Franklin, and he is not the less entitled to the credit of originating it, that after fully considering the subject, he cautiously concluded, that the then state of knowledge of it was hardly ripe for making any hypothesis. 'I think we want more and a greater variety of experiments in different circumstances, to enable us to form a thoroughly satisfactory hypothesis.' The demonstration of the hypothesis, if it is considered conclusive, is sufficient distinction, and belongs to a more advanced state of science than the eighteenth century could boast. The credit of originating it we should abandon. "I have not the least doubt that when these observations of Professor Bache, reach the eye of Professor Phillips, it will give him little or no uneasiness, to find that such an accurate observer as Dr. Franklin had preceded him in an hypothesis. The Doctor's remarks were continued in a letter to Dr. Percival, who has also written on the subject, and first published in the Manchester Memoirs for 1784."-Extract from a Letter to the Editor, April, 1836. * There is a curious anachronism committed by the author of the article in the Magazine of Popular Science, entitled "Recent Researches on the Formation of Rain." He states that the experiments of Dr. Heberden on this subject confirm the recent ones of M. Arago, whereas Dr. H's experiments must have been made before the latter philosopher was born! Deserving Pensioners. If the word "Pension" be correctly defined to be " an allowance made to any one without an equivalent,* it is high time another was substituted, to designate that reward which a nation decrees for services already performed; and also that the following names, so triumphantly and properly introduced by Mr. Spring Rice, the Chancellor of the Exchequer, in his recent speech on the "Pension List," should at least be erased from that catalogue, and placed on a very different roll. On Mr. Whittle Harvey having challenged the government to produce ten names of intellectual merit on the Pension List, the Chancellor of the Exchequer replied:-"I have been challenged to show ten names on the Pension List that have been distinguished for their public services, or for eminence in literature, in science, or in any other way that could possibly be a recommendation for their being placed on that list. Now I accept that challenge. The list I am about to give contains the names of Dr. Dalton, Mr. Ivory, Mr. Airy, Mrs. Somerville, Dr. Southey, Mr. Montgomery, and, if I chose, I could go on and double the List." It is so rarely that science or any of her votaries, receive attention from an English minister, that it is with new and grateful feelings that we give the above extract, we must also observe that it is curious to see how quickly the politician was aware of the advantage of his position, in being prepared to quote even so small a number of really-deserving pensioners. We have great hopes that his sagacity will early induce him to strengthen it still more. Nebula. "THE discoveries as to the nature of the bodies of our solar system, which the use of the telescope presented to its first inventors, must have been unexpected, and in no small degree astonishing. Yet we may safely assert, that they exhibit no remarkable novelty. The ring of Saturn alone can be considered as materially different from the objects constantly before our eyes. In all the other planets we see bodies similar in shape to our earth, analogous (as we have good reason to believe) in internal constitution, revolving in like manner, enlightened by the same principal luminary, and by similar satellites, the subjects and the exciters of similar attractions, and possessing at least some similarity in the construction of their surfaces, and in the phenomena of their atmospheres, as far as spots and belts enable us to conjecture. Everything, in fact, leads us to conclude that they are bodies of the same order: that, with specific differences, there is a generic resemblance; that the circumstances of formation, which have bound all in one mechanical system respecting the sun as the principal seat of force, have also impressed upon all one physical system, as testified by the similar arrangement of subordinate bodies, and the probable resemblance of their gaseous as well as their solid parts. But, when we look into the sidereal world, the analogy of system fails entirely. A star, it is true, may be conceived analogous to our sun: a double star, forming a binary system, though we have nothing here exactly like it, is still not remarkably different in its nature from a single one: but a star, * Walker's Dictionary, edit. 1822. |