December 22, 1892] 



NATURE 



m 



The success of this comparatively new industry has been so 

 marked, that, as a natural result, competitors with rival pro- 

 cesses have come forward. Some of these met with failure at 

 an early stage of their career, but others are supplying oxygen 

 to the public. This is by no means a state of things to be 

 deplored from the consumer's point of view, if the product from 

 the one source is as good as the other, for benefit generally arises 

 from healthy competition. But when the rival product turns out 

 to be not oxygen, but a half and half mixture of oxygen and 

 air, with a slight excess of the latter, the competition is of a 

 decidedly unhealthy character, and is correspondingly bad for 

 the consumer. I recently obtained a sample of gas from a 

 dealer, which on testing (with a Hempel absorption pipette, 

 charged with metallic copper and ammonia) I found to be a 

 mixlure containing only 60 6 of oxygen. I next tested the 

 illuminating value of this highly-diluted oxygen with a limelight 

 jet, and for sake of comparison, placed by its side a precisely 

 similar jet supplied with Krin's oxygen, and, as might have been 

 expected, the light given by the form'er was little more than one- 

 half as intense as that afforded by the latter. With the good 

 oxygen the lime cylinder was quickly pitted, whilst the ether 

 showed no symptom of destruction. It is also to be remarked 

 that the consumption of the diluted gas was, for a given period, 

 about one-third more — striving with both jets to get the best 

 possible light — than that of good oxygen. On the same principle 

 a mountaineer at a high altitude will pass more (rarefied) air 

 through his lungs than he will when he is in the valley breathing 

 that which contains the normal quantity of oxygen. 



As this matter is of great importance to many workers, I 

 trust that you may be able to find room in your valued publica- 

 tion for these words of necessary caution. 



T. C. Hepworth. 



45, St. Augustine's Road, Camden Square, N.W., 

 December 6. 



THE STAR OF BETHLEHEM. 

 T N the A strottomical Journal of November 26 we 

 ■*■ find the second of two very interesting articles written 

 by Mr. J. H. Stockwell, bearing on the chronology of 

 certain ancient events. In the introduction the author 

 discusses and sums up some of the more important and 

 historical dates which he has determined by calculations 

 of ancient eclipses. He next refers to the help which may 

 be obtained in the same direction by means of calculations 

 of conjunctions of the planets, and quite appropriately 

 to the present season points out that the appearance of 

 the star of Bethlehem may have been due to the conjunc- 

 tion of the planets Venus and Jupiter, instead of Saturn 

 and Jupiter, as was suggested on incomplete data by 

 Kepler nearly three hundred years ago. We cannot do 

 better than lay this part of Mr. Stockwell's communica- 

 tion before our readers. 



" Although the heliocentric conjunctions of the planets 

 occur with a considerable degree of regularity, and are 

 also very easily calculated, the geocentric conjunctions 

 are subject to many inequalities in the periods of their 

 successive occurrences ; so that it requires somewhat 

 elaborate computations to determine accurately the 

 character of any geocentric conjunction of two planets 

 which occurred in ancient times. On account of the 

 frequency of planetary conjunctions, and the indefinite 

 manner in which they are usually described, it becomes 

 a matter of very great difficulty to identify any particular 

 conjunction unless it is associated with some other event 

 whose data can be independently determined. A re- 

 markable case of this character is given in the Bible, for 

 Matthew informs us in the days of Herod the King 

 ' there came wise men from the East to Jerusalem say- 

 ing, " Where is he that is born King of the Jews ? for we 

 have seen his star in the East, and are come to worship 

 him."' From the subsequent inquiries and mandates of 

 Herod the King concerning the time when the star 

 appeared, we are led to infer that its appearance took 

 place within two years preceding the death of Herod, 

 NO. 1208, VOL. 47] 



and it has been sought to explain the appearance of the 

 star by means of a conjunction of the planets— the Creator 

 employing celestial phenomena to proclaim ' the good 

 tidings of great joy, which shall be to all people.' 



" The illustrious Kepler was the first to suggest that the 

 star of the wise men might be explained by means of a 

 conjunction of the planets Jupiter and Saturn, and he 

 even undertook to calculate the times when such con- 

 junctions took place. Much has been said and written 

 on the subject of the 'star of the wise men' during the 

 past few years ; but no important contribution to the 

 natural history of the star has been made since the days 

 of Kepler, nearly three hundred years ago. But the 

 supernatural history and functions of such a star have 

 been discussed in a very able and interesting manner by 

 many writers in theological, literary, and semi-scientific 

 periodicals during the past twenty years, and perhaps 

 nothing of interest and importance can now be added to 

 what has already been published on that subject. 



" I find, however, that Kepler overlooked one important 

 element of the problem in his calculations, and conse- 

 quently left the natural history of the problem in an in- 

 complete and unsatisfactory condition. I shall therefore 

 here attempt to complete more fully what Kepler began, 

 and show that the Biblical narrative concerning the 

 ' star in the east ' is better satisfied by a conjunction 

 of Venus and Jupiter than by any of the conjunctions 

 computed by Kepler. 



" We have already seen that the death of Herod took 

 place early in the year B.C. 4, and if we can now show 

 that there was a very conspicuous conjunction of two 

 bright planets, visible only in the east, within two years 

 preceding that date, the hypothesis that such conjunction 

 was the event referred to in the Biblical narrative will at 

 least be rendered plausible, if not entirely legitimate ; 

 and for this purpose I have here undertaken the calcula- 

 tion of all the conjunctions of the planets which took 

 place near that epoch. I shall first enquire whether there 

 was a conjunction of the planets Jupiter and Saturn about 

 that period of time which would satisfy the required con- 

 ditions. The mean interval between two heliocentric 

 conjunctions of Jupiter and Saturn is 7253'4638 days ; 

 and they were in mean conjunction B c. 6, January 30. 

 Now the time of true heliocentric conjunction may differ 

 from the time of mean heliocentric conjunction by 241 

 days, on account of the inequalities m their elliptic 

 motions, and by 23 days more by reason of the great 

 inequalities of long period in their mean motions. But 

 the time of geocentric conjunction of Jupiter and Saturn 

 may differ from the time of heliocentric conjunction by 

 102 days ; so that a geocentric conjunction may occur 

 one whole year before or after the time of mean helio- 

 centric conjunction. In the present instance I find that 

 the true heliocentric conjunction took place B.C. 7, Sep- 

 tember 23, which is 129 days before the mean helio- 

 centric conjunction ; and that there were three geocentric 

 conjunctions during the year B.C. 7, which took place as 

 follows : — 



" The first conjunction took place June 7, in which 

 Saturn passed i'' 4' to the south of Jupiter ; the second 

 conjunction took place September 18, in which Saturn 

 passed i'^ 2' to the south of Jupiter ; and the third con- 

 junction occurred on December 15, in which Saturn 

 passed 1° 8' to the south of Jupiter. 



" In the first conjunction the planets would have an 

 elongation of about 73"" to the westward of the sun, and 

 would be seen during four or five hours in the east in the 

 morning. The second conjunction took place near the 

 time of opposition with the sun, and would be visible 

 during the whole night, so that it could not properly be 

 designated as a star in the east any more than a star in 

 the west. In the third conjunction the planets would 

 have an elongation of about 84° to the eastward of the 

 sun, and could therefore appear only as evening stars 



