March 19,, 1896] 



NATURE 



475 



have to be calculated for certain suitable and equidistant in- 

 tervals of time. Knowing the hourly movements of the moon 

 in right ascension and polar distance for the same instants from 

 the almanack, and the elements of the phenomena, whether it 

 be eclipse or occultation, the tracing of the positions of the bodies 

 may be proceeded with. The plane of the drawing is supposed 

 to represent that plane which is at right angles to the line join- 

 ing the centre of the moon and the observer, at any one of the 

 chosen instants near the time of conjunction of the two bodies. 

 On this plane the successive projected true and apparent positions 

 of the two bodies, sun and moon, or moon and star, are con- 

 sidered. The line passing through the centres of the moon in 

 her different positions will thus represent the apparent lunar 

 orbit, and if in addition we know the position at the moment 

 of true conjunction of the two bodies, occupied by the centre of 

 the sun or star, according as we are dealing with an eclipse or 

 occultation, it will be easy to find the positions of the centres 

 at the moments of contact, or of immersion and emersion, and 

 also the times. 



The calculation of the elements necessary for making the 

 drawing would have for its aim the determination of the co- 

 ordinates of the points of the apparent orbit occupied by the 

 centre of the moon. This work is here rendered very easy by using 

 the series of tables which have been prepared for reducing the 

 calculation to a minimum. As an illustration showing the method 

 of procedure, Mr. Cruls gives two complete worked-out cases, 

 one of the eclipse of the sun at Rio de Janeiro April i6, 1893, 

 and another of the occultation of a Virginison March 22, 1894, 

 at Cireenwich. The accuracy of this graphical method may be 

 gauged from the observed minus calculated values obtained in 

 the two cases just mentioned. 



Eclipse of the f ist contact .. 

 sun \ 2nd ,, 



■2-41 

 ■0-3/ 



Observed — Calculated. 



Occultation of / Disappearance -t- o 8 \ Nautical Almanac- 

 o Virginis (Reappearance +i'2} Graphical Method. 



PENDULUM OBSERVATIONS IN GERMANY. 

 TT is a well-known fact that, at different places on the earth's 

 -*■ surface and at the same sea-level, pendulums change their 

 rates of swing. The numerous observations of von Sterneck, made 

 in the region of the Alps, suggested that such deviations from 

 the normal might be, and were most probably, explained on the 

 supposition of unequal distributions of the masses in the 

 neighbourhood — that is, either inside the mountains or in the 

 earth's crust itself. Such observations as these indicated that 

 good work might be done in this direction, and in consequence 

 measurements were made on Mont Blanc, while in other 

 directions observations were being organised by the scientific 

 societies in Vienna, Miinchen, Leipzig, and Gottingen. The 

 gravity determinations on Mount Blanc were made at the new 

 observatory, and M. Jannsen informs us that besides those 

 made in Chamounix in the previous summer, and on the Grands 

 Mulcts (3050 metres elevation), by M. Bigourdan, an effort will 

 be made to continue them this summer on the summit itself. 

 The results which have been obtained up to the present are as 

 yet unpublished. A region which appeared full of interest for 

 investigating the different rates of swinging pendulums is that 

 in the region of Gottingen and the Harz ^iountains. Prof, von 

 Kcinen singled out what he thought ;vere the three most suitable 

 spots on account of their different geological conditions for such 

 investigations, and observations at these Stat ions were all compared 

 with those made at Gottingen, this being the chief observing 

 station on account of the observatory. It is true that the 

 instrument employed in these determinations was far too rough 

 for accurate and reliable measurements, it being the one which 

 Dr. von Drygalski had previously used on his Greenland 

 expedition, and with which Sterneck made his first experiments. 

 The actual observations wer.e made by Prof Wilhelm Schur and 

 Dr. Grossmann, and the results were communicated to the 

 Nachrichten der K. G. der Wiss. Gott., Heft 2, 1895. These 

 may be summed up as follows. In the cases of the two 

 stations at Griinenplan and Teichmlihle, the very small differences 

 when compared with Ciiittingen may be neglected when the kind 

 of instrument employed be taken into consideration. The 

 <lifference for the station Sack, on the other hand, was com- 

 jiaratively large, the numbers being — 



For Griinenplan S.ick Teichmiihle 



-0-00018 ... - o-ooo8i ... -000028 



The conclusion drawn by Prof, von Konen from this some- 

 what rough determination was that the diminution in the intensity 

 of gravity for the station Sack might pos.sibly be due to the 

 present condition of the positions of the underlying superposed 

 strata (Schichteniiberschiebung). 



Since the above determinations were made, the same ground 

 has been covered, in September and October last, by Herr 

 Haasemann, who, at the request of Geheimrath Helmert, under- 

 took to make a series of measurements at the .same observing 

 stations as used by Prof. Schur. In this new investigation the 

 instruments employed were more accurate and of later design, 

 so that the results may be looked upon as more trustworthy and 

 accurate. Limiting ourselves to giving the actual numerical 

 results, the differences for the three stations when compared as 

 before with Gottingen were — 



For Griinenplan Sack Teichmiihle 



-f 0-00007 ... - o "00003 ••• - o'ooon 

 Comparing these figures with those obtained by Prof. Schur, the 

 large difference for Sack entirely disappears. This indicates 

 that at these places the determinations of the rates of the 

 pendulums give no trace of any variation in the intensity of 

 gravity, or at least of any variation which is capable of being 

 detected by the apparatus employed. D. 



PETROLEUM LAMP ACCIDENTS. 

 'T'HE report of Mr. Alfred Spencer, chief officer of the Public 

 Control Department of the London County Council, as to 

 the causes of petroleum lamp accidents, and as to the measures 

 necessa'ry for preventing them, which has just been issued, is an 

 important document. The number of accidents due to the use 

 of cheap and unsafe petroleum lamps has assumed alarming pro- 

 portions within the past few years, that the means by which the 

 accidents can be prevented cannot be too prominently or too 

 frequently brought before the public. Mr. Spencer has made a 

 thorough investigation with numerous lamps and stoves in which 

 petroleum is used, in order to determine the conditions of safety. 

 The results of his experiments lead him to conclude that raising 

 the flash-point fixed by the Petroleum Acts would not alone be 

 effectual in preventing lamp accidents, as this would not prevent 

 the sale and use for illuminating purposes of oil below that 

 flash-point. He remarks, however, that the prohibition of the 

 retail sale, and the prevention of the use for illuminating purposes 

 of mineral oil below a flashing-point sufficiently high to prevent 

 all lamp accidents, would be effectual if it were practicable. The 

 prohibition by statute of the sale of unsafe lamps would be another 

 means of putting an end to lamp accidents, as both experience 

 and experiment have proved that mineral oils, such as are now in 

 common use, can be safely burnt in properly constructed lamps. 

 The difticulties in the way of prohibiting the sale of unsafe oil 

 are far greater than would be met in regulating the construction 

 and sale of safe lamps ; therefore Mr. Spencer suggests that the 

 latter is the means of safety which should be enforced by order 

 of the Secretary of State. His suggestions for the safe con- 

 struction and proper management of lamps, revised in the light 

 of recent experiments, are as follows : — 



Construction. 



(i) The oil reservoir should be of strong metal, properly 

 folded and soldered at the joint, and should not be of china, 

 glass, or other fragile material. 



{2) There should be no opening between the reservoir and the 

 burner, other than through the tube which holds the wick ; and 

 this tube should be extended to within \ in. of the bottom of the 

 reservoir, and should have no opening into the reservoir except 

 at its base. 



(3) The burner should be securely attached to the reservoir, 

 preferably by means of a strong and well-made screw attach- 

 ment. 



(4) There should be no openings through which oil could flow 

 from the reservoir should the lamp be upset. 



(5) Every table lamp should have a broad and heavy base, to 

 which the reservoir should be strongly attached. 



Wicks. 



(6) Wicks should be soft, and not tightly plaited, and should 

 quite fill the wick-tube without having to be squeezed into it. 



(7) Wicks should be frequently renewed, and before being put 

 into lamps should be dried at a fire and then immediately soaked 

 with oil. 



NO. 1377, VOL. 53] 



