Sun will produce the effect of a band across it. Supposing the lower line of the band were to be on the centre of the Sun, and the upper line to be half way between the centre and the top (and we were able to ascertain that this was so), we could by other means as well as by simply multiplying the 18,000 miles by two or four, as mentioned above, ascertain its breadth; that is to say, if each of the two observers noted down the exact time it took the planet to cross the Sun at their respective stations, they would, on comparing notes when they met, be able to tell what difference there was between the two times. The difference might (say) be a quarter of an hour or it might be half an hour, and supposing the transit occupied five hours at the centre (which would, of course, be the longest of the two times), then the difference would be a twentieth or a tenth, as the case might be. The lines of the band being made by one planet, and their existence, being owing only to the difference of position of the observers, it is of course obvious that the difference of times would necessarily be equal to the difference in length of the lines of the band; the difference in length, therefore, will be also one-tenth or onetwentieth, as the case may be, under the above hypothesis.

Were the planet to cross the Sun, as observed from the two positions, at an equal distance on both sides of the centre of the Sun, there would of course be no difference whatever between the two times, and the

transit would be useless to us as proving, by means of the difference of times, what the diameter of the Sun is. As mentioned above, however, the band is a narrow one, comparatively speaking, and entirely on one side of the centre. Consequently there is a diffe

rence between them.

Before, however, the difference can be made use of for the purpose of measuring the diameter of the Sun, it is obvious that the points of the circumference of the Sun where the planet enters upon it, as seen from the two positions, should be carefully noted. For, of course, the nearer the centre the lines made by the planet are, the less the difference there can be between them the further they are from the centre the greater will be the difference-this will be seen at once. Were one of the lines on the centre, and the other only to touch the top, then the difference would practically amount to half the whole time, inasmuch as it would not be till the planet had reached the centre of the disc of the Sun, as seen from one position, that it would touch the top of it as seen from the other position; and the difference of the lengths of the lines being precisely the same as the difference of times, and the difference in times being one half the difference in length, it would also be one half. Again, were the observer in the Northern Station to see the planet passing across the centre as before, and the observer in the South to see it passing half way between the centre and the top, by the same reasoning the differ

ence would be a quarter of the whole time. We must therefore take care to note as nearly as we can about where on the Sun the planet meets it as seen from the two stations.

Now what is the inference to be derived from the facts as we have stated them? It is obvious that no two circles of different size can have the same diameter. It is equally obvious that a line drawn across a circle parallel to a line drawn through its centre, cannot possibly be equal in length to a line drawn in precisely the same place across another circle the diameter of which is greater or less than the diameter of the first circle, for if it were so the circumference of a circle would not be uniform. This being so, it is easy to see that the difference between the lengths of two lines drawn across one circle parallel to a line drawn through its centre, at any stated distance apart, cannot possibly be equal to the difference between the lengths of two lines drawn in the same position and the same distance apart, across any other circle in which the diameter differs from the first circle. In other words, the difference between the lengths of the two lines drawn across a circle, at a stated distance apart, and at a particular distance from the centre, is the key to the problem, what is the breadth or diameter of the circle. Having satisfied ourselves as to this, we ask the question, What is necessarily the diameter of a circle across which two lines, 18,000 miles apart, and drawn in the particular positions Venus has been observed

from the two stations to travel, differ from each other in length to the extent they have been found to differ, and it is plain this is to be ascertained on the principle of Rule of Three sum.

Having ascertained the diameter of the Sun in this way, all that remains to be done is to ascertain its distance from us, and this is done by comparing its actual diameter with its apparent diameter. There is no more difficulty in doing it than in ascertaining the distance of a church steeple a great way off when you know its height.

Before closing this little essay it may be as well to explain that it would be impossible to obtain a base line of 7,000 miles on exactly the same meridian. This, however, will complicate the observation very little, as all that is necessary under such circumstances is to make proper allowance for the time of day.

OF

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MARCH.-A COMPARATIVE GRAMMAR OF THE ANGLO-SAXON LANGUAGE; in which its forms are illustrated by those of the Sanskrit, Greek, Latin, Gothic, Old Saxon, Old Friesic, Old Norse, and Old High-German. By FRANCIS A. MARCH, LL.D. Demy 8vo, cloth, pp. xi. and 253. 1877. Price IOS.

MARCH.-INTRODUCTION TO ANGLO-SAXON. An Anglo-Saxon Reader. With Philological Notes, a Brief Grammar, and a Vocabulary. By FRANCIS A. MARCH, LL.D. 8vo, cloth, pp. viii. and 166. 1870. Price 78. 6d.

HARRISON AND BASKERVILL.

HANDY DICTIONARY OF ANGLOSAXON POETRY, based on Groschopp's Grein. Edited, revised, and corrected, with Grammatical Appendix, List of Irregular Verbs, and Brief Etymological Features. By JAMES A. HARRISON, Professor of English and Modern Languages in Washington and Lee University Virginia; and W. M. BASKERVILL, Ph.D. Lips., Professor of English Language and Literature in Vanderbilt University, Nashville, Tenn. Demy 8vo, cloth, pp. 318. 1885. Price 128.

RASK. GRAMMAR OF THE ANGLO-SAXON TONGUE, from the Danish of Erasmus Rask. By BENJAMIN THORPE. Third Edition, corrected and improved, with Plate. Post 8vo, cloth, pp. vi. and 191. 1879. Price 58. 6d.