Sept. 7, 1883.] 



♦ KNOWLEDGE ♦ 



157 



sented the ecliptic or sun's path, only it must be remem- 

 bered that the moon's path round the celestial sphere never 

 does coincide with the sun's path, but is always inclined 

 about 0° 8' thereto. 



Let Z N Z' S, Fig 2, represent the celestial sphere, other 

 letters representing the same things as before, but M O m, 

 inclined 23 J° to the equator E O E', representing the moon's 

 path when at about its mean inclination to the equator. 



Then in each sidereal month the moon (when at her 

 mean inclination, and neglecting slight changes which her 

 path is always undergoing) travels once round the path 

 M III, passing from O in the farther hemisphere to M, 

 thence to in the mean hemisphere, to m, and to O in the 

 farther hemisphere as before. When she is at O, whether 

 on the farther or mean hemisphere E E', the equator 

 represents her diurnal course, O E (from eastern to 

 western O) being the above - horizon half, O E' O (from 

 western O to eastern O) being the below-horizon half. 

 She takes about 1 day 501 rain, in being carried once 

 round, her own motion the other way causing the 

 mean lunar day to be 50.\ min. longer than the mean 

 solar day. Of course the moon's motion in a day, 

 solar or lunar, carries her considerably away from O, so 

 that she never does actually complete such a circuit as we 

 have just imagined. That is the circuit she would com- 

 plete if she remained the whole day on the equator E O E'. 

 As a matter of fact if she were at O at the beginning of a 

 diurnal circuit she would have got to n or to 7i' at the end 

 of that time, by her monthly motion along her own path 

 M O III ; at n if she were passing from O on the farther 

 hemispliere ascendingly or northwards from the equator ; 

 at w', if she were passing descendingly or southwards from 

 the equator point O on the nearer hemisphere. Her real 

 course would be a spiral approaching P or P' from E O E' : 

 but we need not specially concern ourselves with this 

 consideration. 



When, a week after being at (on the farther hemi- 

 sphere, suppose), the moon has passed to M on her own 

 path, her diurnal course is the circle M C m', of which only 

 the small part represented by K m' (or projected into K in') 

 lies below the horizon. A week later she is at again : 

 a week later at m : and now her diurnal circuit is projected 

 into M'C'ot, of which only the part represented by M'L (or 

 projected into M'L) is above the horizon. A week later 

 still she is again at O. Her real diurnal path is a spiral 

 ranging between the parallel planes M C m' and M'0')». 



I have here said a week, when strictly I should have 

 said a quarter of a sidereal lunar month, or of the time 

 in which the moon completes the circuit of the stellar 

 sphere. As a lunar sidereal month lasts 27/, days or there- 

 abouts, each fourth of the circuit lasts about G^ days, or 

 not quite a week. 



It is to be noticed moreover that when, as indicating 

 with such proV>lems as the harvest moon, we consider the 

 successive rising.^, southings, and settings of the moon we 

 are dealing really with the lunar day. Lunar days vary, 

 indeed it is their variation which has chielly to be con- 

 sidered in discussing the harvest moon : but of mean lunar 

 days, there are only about 2GA in a sidereal lunar month, 

 and about 261 in a lunation. In fact in the lunar month 

 the number of lunar days is one less than the number of 

 solar days, the moon losing one diurnal circuit per lunation 

 as compared with the sun. 



We are now in a position, knowing what are the moon's 

 movements without reference to phase, to determine what 

 they will l)e in any given month when her phase at the 

 tinu! she is at any point of her own orbit, is known. 



(To he concluded in our next.) 



d^bituarp. 



DEATH OF PROFESSOR TOBIX. 



WE learn with sorrow of the death of Professor Thomas W. 

 Tobin, at Louisville, Ky. He will be well remembered by- 

 many in this countiy as a fellow-worker of Professor Pepper's at 

 the Polytechnic ; but obtained a wider and more enduring reputa- 

 tion in America as the inventor of the sine pendulum, and as a 

 skilful exponent of scientific truths. He was bom in January, 

 1844, in London, so that he was not quite forty years old when he 

 died, on Saturday, August 4th last. He went to America twelve 

 years ago with Professor Pepper, and resolved to stay in that 

 country when Professor Pepper, disheartened by failure, returned 

 to England. The Legislature of Kentucky made an appropriation 

 of SSdO for the construction of one of Tobin's sine pedulums, and 

 Colonel Young was appointed as Commissioner to take charge of 

 it when it was exhibited at Paris. The pendulum is now in the 

 Agi-icultural and Mechanical College, Richmond, Ky. The Poly- 

 technic Institution, Louisville, Ky., was founded chiefly through 

 the exertions of Professor Tobin, Dr. Stuart Robinson, and Colonel 

 Bennet H. Young. Professor Tobin was appointed scientific 

 lecturer there, and held that position till the time of his death. 

 Crowded audiences attested his skill in the art (more difficult than 

 is generally thought) of so interpreting science as to interest the 

 unscientific. Professor Tobin was a genial man, of companionable 

 manners, wide-reading, and cultured tastes. He died of con- 

 sumption, a disease to which his mother and all his brothers and 

 sisters had already succumbed. 



A Cable for Cochin-China. — The recent operations of 

 the French in Tonquin have directed public attention to 

 that part of the globe ; but it is not generally known that 

 the Eastern Extension Telegraph Company have for some 

 time past made arrangements for laying a submarine cable 

 between Tonquin and Cochin-China. It was intended to 

 lay the cable from Saigon, where communication already 

 e.xists, and Hai-Phong with a branch into Hanoi. Unfor- 

 tunately, however, the French Chamber has rejected tie 

 proposals of the English company in favour of a less ad- 

 vantageous offer by M. Blanscube, deputy of Cochin-China. 

 The Colonial Council of that possession have proposed to 

 share the expense of constructing the new line, which 

 there is every reason to believe will be made by French 

 manufacturers and laid in French territory. — Engineerivij. 



A MEETING of the subscribers to the parliamentary fund 

 of the Manchester Ship Canal was held on Tuesday week 

 at Manchester. It was reported that the committee had 

 received from subscribers £40,778, and that the ex- 

 penditure amounted to -£47,510. The committee were of 

 opinion that another application to Parliament would be 

 successful. A motion was passed expressing regret at the 

 action of the Committee of the House of Lords in stopping 

 the Bill. The provisional committee was empowered to 

 promote the Bill in the ensuing session of Parliament, in 

 such manner as might be found expedient or desirable. It 

 was stated that promises of .£5,000 had been received 

 towards the cost of the second application to Parliament. 



Letters from Athens, says a contemporary, announce 

 an interesting disco\ery, brought to light in the course of 

 some excavations which are being carried out in the Island 

 of Delos by the pupils of the French School at Athens. 

 In the neighbourhood of the Theatre of Apollo, they came 

 upon the remains of a private house, which apparently 

 belonged to the Alexandrine epoch. A court surrounded 

 by pillars and twelve chamliers lias been opened out The 

 floor is composed of mosaic, which is a fine specimen, 

 representing flowers, fishes, and other ornaments. In the 

 middle of the court is a well, now quite choked up. The 

 door of the house, and the line of roadway or street lead- 

 ing to it, have also been discovered. The excavations will 

 be continued, and it is hoped that a large portion of the old 

 town will be brought to light. 



