104 



NATURE 



[June 2, 1892 



by merely subtracting the weight of the globe when 

 empty from the weight when full. When the globe is 

 empty, its external volume is less than when full, and 

 thus, in order to obtain the true weight, the apparent 

 weight of the gas must be increased by the weight of air 

 whose volume is equal to the change of volume of the 

 globe. 



In order to determine the amount of this change of 

 ^olume, the globe is filled to the neck with recently boiled 

 distilled water, and the effect is observed upon the level 

 in the stem due to a suction of, say, 20 inches of mercury. 

 It is not advisable to carry the exhaustion much further, 

 for fear of approaching too nearly the point at which 

 bubbles of vapour may be formed internally. In the 

 earlier experiments, described in the preliminary note, 

 the upper surface of the liquid was in the stem of the 

 globe itself (below the tap), and the only difficuhy lay 

 in the accurate estimation of a change of volume occur- 

 ring in a wide and somewhat irregular tube. The method 

 employed was to produce, by introduction of a weighed 

 quantity of mercury, a rise of level equal to that caused 

 by the suction. 



The advantage of this procedure lay in the avoidance 

 of joints and of the tap itself, but, for the reasons given, 

 the readings were not quite so accurate as might be 

 desired. I wished, therefore, to supplement, if possible, 

 the former determination by one in which the change 

 of volume occurred in a tube narrower and of better 

 shape. With this object in view, the stem of the globe 

 was prolonged by a graduated tubular pipette attached 

 with the aid of india-rubber. The tubes themselves were 

 treated with gutta-percha cement, and brought almost 

 into contact. It ha'd hardly been expected that the joint 

 would prove unyielding under the applied suction, but it 

 was considered that the amount of the yielding could be 

 estimated and allowed for by operations conducted with 

 tap dosed. The event, however, proved that the yielding 

 at the joint was scarcely, if at all, perceptible. 



The pipette, of bore such that 16 cm. corresponded to 

 I c.c, was graduated to o-oi, and was read by estimation 

 to 0001 c.c. In order the better to eliminate the changes 

 due to temperature, readings under atmospheric pressure, 

 and under a suction of 20 inches of mercury, were alter- 

 nated. On January 28, 1892, a first set gave 0-648- 

 0-300 = 0-348 ; a second gaveo-6645— 0-316 = 0-3485 ; and 

 a third gave 0-675 - 0-326 = 0-349. Similar operations 

 with tap closed ^ gave no visible movement. 



The result of the day's experiments was thus 0-3485 

 for 20 inches, or 0-523 for 30 inches, suction. Similar 

 experiments on January 28, at a different part of the 

 graduation, gave 0-526. On this day the yielding with 

 tap closed was just visible, and was estimated at 0001. 

 As a mean result, we may adopt 0-524 c.c. The gradua- 

 tion of the pipette was subsequently verified by weighing 

 a thread of mercury that occupied a measured length. 



A part of the above-measured volume is due to the ex- 

 pansion of the water when the pressure is relieved. We 

 may take*this at 0-000047 of the volume per atmosphere, j 

 The volume itself may be derived with sufficient accuracy 

 for the present purpose from the weight of its oxygen 

 contents. It is 2-5 17/0-001 37, or 1837 c.c. The expan- 

 sion of the water per atmosphere is thus 0000047 X 1837, 

 or 0-087 c.c. This is to be subtracted from 0-524, and 

 leaves 0437 c.c. This number applies strictly to the 

 volume inclosed within the glass, but the change in the 

 external volume of the globe will be almost the same. 



The correction now under consideration is thus the 

 weight of 0-437 c.c. of air at the average temperature of 

 the balance room. The density of this air may be esti- 

 mated at 0-00122 ; so that the weight of 0437 c.c. is 

 0-000533 gram. This is the quantity which must be 

 added to the apparent weights of the gases. The former 



estimate was 0-00056 gram. The finally corrected weights 

 are thus— ^ 



H = 0158531, = 2-51777; 

 and for the ratio of densities we have 

 15-882. 



This corresponds to a mean atmospheric condition of 

 pressure and temperature. 



If we combine the above ratio of densities with Prof. 

 Morley's ratio of volumes, viz. 2-0002 : i, we get, as the 

 ratio of atomic weights, 15-880. 



If we refer to the table, we see that the agreement of 

 the first and third series of hydrogen weighings is very 

 good, but that the mean from the second series is de- 

 cidedly lighter. This may have been in part fortuitous, 

 but It IS scarcely probable that it was so altogether. 

 Under the circumstances we can hardly reckon the 

 accuracy of the final results as closer than .^^q-^. 



The accompanying table of results, found by various 

 experimenters, may be useful for comparison :— 



THE ORIGIN OF THE YEAR} 



II. 



Difficulties. 



nr HERE no doubt was a time when the Egyptian astro- 



*■ nomer- priests imagined that, by the introduction of 



the 365-days year, beginning at the solstice or the nearly 



contemporaneous Nile flood (there is an interval of three 



days between them in the present Coptic calendar 2), and 



by marking the commencement, in addition, by the heliacal 



rising of one of the host of heaven, they had achieved 



finality. But alas ! the dream must soon have vanished. 



Even with this period of 365 days, the true length of 

 the year had not been reached; and soon, whether by 

 observations of the beginning of the inundation, or by 

 observations of the solstice in some of the solar temples 

 which, beyond all doubt, were then in existence, it was 

 found that there was a difference of a day every four 

 years between the beginning of the natural and of the 

 newly-established year, arising, of course, from the fact 

 that the true year is 365 days and a quarter of a day 

 (roughly) in length. 



The true year and this established year of 365 days, 

 then, behaved to each other as follows. Let us take a 

 year when the solstice, representing the beginning of the 



' Continued from vol. xlv. p 490. 



- The calendar in question (given both by Brugsch and De RougO 'Si 



It is goo I for the neigh- 



For greater security the tap 

 suction. 



turned while the interior was under 



NO. I I 79, VOL. 46] 



doubtless, a survival froti old Egyptian 



bourho-id of Cairo, and the relation of the important days of the inundatFon 



to the solstice, in that part of the river, is as follows : — 



Night of the drop 11 Payni 



Beginning of the inundation ... 18 „ 



Assembly at the Nilometer ... 25 ,, 



Proclamation of the inundation ... 26 ,, 



Marriage of the Nile 18 Mesori 



The Nile ceases to rise 16 Thoth 



Opening of the dams ... 17 ,, 



End of the greater inundation ... 7 Phaophi 



Summer solstice. 

 3 days after. 



