July 1 1, 1889] 



NATURE 



261 



has the biquartz. Two strips of heavy-glass of exactly equal 

 length and similar quality, such as those I hold in my hand, 

 must be introduced in the respective paths of the two beams : 

 and one at least of them must be surrounded by a magnetizing 

 coil. The biquartz has wiped out the interference fringes ; but 

 on magnetizing one of the two pieces of heavy-glass, or on 

 magnetizing the two in opposite senses, the interference bands 

 can be made to reappear. It is in this way that Prof. Sohncke's 

 experiment — hardly suitable for a lecture theatre — was per- 

 formed. It is in this way that we establish upon an experi- 

 mental basis the fact that light itself, and not merely the plane 

 of its polarization, experiences an optical torsion when subjected 

 to those forces which, whether crystalline, molecular, or magnetic, 

 exert upon it an optical torque. 



BABYLONIAN ASTRONOMY} 

 II. 

 nPHE year — that is, the period bringing back the recurrence of 

 the seasons — is not a primitive means of dividing time, but 

 the result of many observations. The simplest way of marking 

 time is by seasons, and the system is still employed by some savage 

 nations in Africa, A season does not correspond to one year, 

 and more than one may be in a year ; seasons, however, generally 

 correspond to the year period. As to the division of the year, 

 it must have varied according to the climate and region, but the 

 simplest is by ten, as ten is the most common dividing number, 

 and such was the one originally adopted by the Semites and Egyp- 

 tians. This year of ten months, or rather ten parts, has left 

 traces among the Semites and in classical authors. The 

 Babylonians assimilated their ;first ten kings to the ten parts 

 of the year. At Rome, we are told that the year before Numa 

 Pompilius was composed of ten months only. 



A year of ten lunar months is impossible, for after two or 

 three of such periods it would no longer correspond with the 

 seasons. We find, therefore, that the ten parts of the year were 

 composed of thirty-six days distributed in four periods or weeks 

 of nine days. This last division was not, however, official : the 

 days of each of the ten divisions of the year were merely numbered 

 from one to thirty-six ; it was at a later date that the days 

 received names from the protecting gods attributed to them. 



It is to be noticed that in Egypt the months had no special 

 names ; the year was divided, after the reform of the calendar, 

 into three seasons of four months of thirty days, called first, 

 second, and so on, of the season to which they belonged. 

 Popular names were attributed to them afterwards, taken from the 

 religious festivals, but they do not appear in the texts before the 

 Ptolemaic period. The like took place among the Semites : 

 the months were called first, second, third, and so on, but were 

 not distributed into seasons. It was only after the Akkadian in- 

 vasion that the other names, Nisan, Tyyar, &c., were adopted, 

 and the eighth month never lost its numerical name. In 

 the astronomical omen tablets the primitive nomenclature by 

 numerical order was often preserved. 



It is still uncertain at what time the old calendar of ten 

 divisions of thirty-six days was reformed into one of twelve 

 months of thirty days. The change was due to the desire to mea- 

 sure the time by the appearance of the moon. This reform may be 

 due to the influence of the Akkadians, who made the conquest of 

 Babylon about 7000 B.C. These people had a lunar calendar 

 composed of thirteen months of twenty-eight days, giving, there- 

 fore, a year of 364 days. It was no doubt more accurate than 

 the Semitic calendar, but the Akkadians adopted their subjects' 

 calendar. The deficiency with the normal solar year of 365 days 

 was made up by means of a supplementary month placed ir- 

 regularly by the priests when they thought it necessary. That is 

 why we find various intercalary months, and why, in some cases, 

 as late even as Nebuchadnezzar the Great, they occur in three 

 successive years. To make up the deficiency the Babylonians 

 had also a supplementary day called the "heavy 21st," which 

 could be inserted in any month before the normal 21st. We 

 find the mention of such supplementary days in several con- 

 secutive months. 



The Akkadians, before invading Babylonia, divided their 

 month into four parts or weeks of seven days each. This division 

 had, however, nothing to do at first with the planets, to which 

 the days were assimilated only at a later date. The Akkadians 



Abstract of the second lecture delivered by Mr. G. Bertin at the British 

 Museum. Continued from p. 237. 



looked on the planets as evil spirits disturbing by their irregular 

 motion the harmony of heaven ; and, as evil spirits were the chief 

 objects of their worship, they naturally attributed to each day of 

 the week the name of a planet. When the Akkadians adopted 

 the Semitic month of thirty days, the week of seven days was 

 naturally abandoned in common use, but it was retained for 

 religious purposes with some modification, a new series of f ur 

 weeks commencing with each month. The Semites rejected 

 the Akkadian names of the days of the week, though they pre- 

 served the symbolism attached to them, as is shown by the seven 

 tablets buried under the foundation-stone of Khorsabad. 



Our names of the days of the week are derived from the Akka- 

 dian assimilation of these days to the planets. There is no doubt 

 as to the order in which the planets were assimilated to the 

 names of the days, if we compare them with the colours of the 

 walls of Ekbatana built by a Medic tribe, which preserved the 

 primitive religion of the Akkadians, and also with the tablets of 

 Khorsabad. The following table will show the correspondence : — 



Iron, corresponding to Thursday, or Jupiter, is represented by a 

 red colour, no doubt on account of the rust, which is red. And 

 we must not be surprised to see Venus represented symbolically 

 by black, for Vesper or the Evening Star is really the dusky. 



This proves that the week of seven days, which is found all 

 over Asia and Europe, spread, not from Babylonia, but from the 

 country whence came the Akkadians. 



THE INSTITUTION OF MECHANICAL 

 ENGINEERS. 



n^HE summer meeting of this Institution was held in Paris last 

 week under the presidency of Mr. Charles Cochrane. 



The papers offered for reading and discussion were a de- 

 scription of the lifts in the Eiffel Tower, by Mr. A, Ansaloni, of 

 Paris, supplemented by the results of working to date, communi- 

 cated verbally by Mr. Gustave Eiffel, President of the Societe 

 des Ingenieurs Civils ; the rationalization of Regnault's experi- 

 ments on steam, by Mr. J. Macfarlane Gray ; on warp-weaving, 

 and knitting without weft, by Mr. Arthur Paget ; on gas-engines, 

 with description of the Simplex engine, by Mr, E. Delamare- 

 Deboutteville ; on the compounding of locomotives burning 

 petroleum refuse in Russia, by Mr. T. Urquhart ; and descrip- 

 tion of a machine for making paper bags, by Mr. Job Duerden. 



In the discussion of the first paper, which, as its title shows, 

 was mainly technical in character, the interesting meteorological 

 circumstance of the Eiffel Tower acting as a thunder-cloud 

 discharger was referred to ; clouds laden with electricity having 

 passed quietly over the region of the tower, which previously and 

 afterwards flashed with lightning. It was also pointed out that the 

 perpendicularity of the building is not affected by temperature 

 variations, nor by any wind pressure hitherto recorded. 



We have not received a copy of the paper by Mr. Gray, who 

 reserves the right of reproducing it, but from the syllabus of 

 papers published by the Institution of Mechanical Engineers, it 

 may be stated that Mr, Gray proposes a new unit of heat^ 

 which he compares with the ordinary water-unit, and a new 

 diagram of energy, which he calls the Theta-phi {6 <p) or temper- 

 ature-entropy diagram, a graphic representation of the Carnot- 

 Clausius fundamental principle, of which the area shows heat- 

 units, the co-ordinates being the temperature, 9, and entropy, <p. 

 He compares Regnault's experimental steam -pressures with the 

 pressures calculated by means of his formulae, showing closer 

 agreement than is obtained by Regnault's most accurate 

 formulae. 



In Mr. Paget's paper the three chief methods of making fabric 

 or cloth or tissue from yarns or threads, viz. ordinary weaving, 

 knitting, and what the author calls warp-weaving, are referred to. 

 The paper describes the method by which shaped goods can be 

 made by warp-weaving, and the machine by which this is. 

 efifected. The machine, which is of a very ingenious character. 



