September i, 1923] 



NA TURE 



145 



difficult to safeguard against, and the loss of oil by 

 ignition of the associated gases during storms is a 

 formidable problem, especially in certain parts of the 

 United States. In the Mid-Continent field, for 

 example, as much as 1,000,000 barrels of oil per 

 annum has been lost in this way. 



Preventive measures consist for the most part in 

 the employment of specially designed storage tanks, 

 the wooden top surmounting the metal body being 

 a favoured form in America. This type of tank 

 is open to the objection that continuity of metal is 

 broken, so that perfect protection from lightning 

 cannot be assured. In this country, all-metal tanks 

 are preferred ; sometimes steam-lines are led to the 

 tops of the tanks for discharging steam freely at the 

 approach of a thunderstorm, though in the case of 

 large tank-farms the method proves impracticable. 

 Tanks are usually built in the centre of sump-holes, 

 while a clearance of 200 feet between the site of each 

 tank is desirable. Probably the most recent method 

 for preventing oil-tank fires is that concerned with 

 the use of " Sealite," an artificial preparation con- 

 sisting of a mixture of glucose, glycerin, calcium 

 chloride, glue and starch. This mixture can be 

 rendered lighter than oil by aeration, and when 

 pumped into the tanks it floats on the oil, thus pre- 

 venting evaporation and also combustion. The 

 better-known " Foamite-Firefoam " system of fire- 

 extinction is only applicable once a fire has started ; 

 this depends on the foaming reaction set up by 

 bringing together alum and licorice, by which carbon 

 dioxide is generated, thus effectively choking the fire. 



Oilfield fire may of course be due to other causes 

 besides lightning ; the friction of the crown-pulley 

 when bailing operations are in progress on the rig ; 

 crossed guy-lines or wires causing sparks which ignite 

 the volatile gases ; the throwing down of lighted 

 cigarette-ends (regarded as a criminal offence in some 

 countries — and rightly so) ; spontaneous combustion 

 of gas-lines ; leaky pipe-lines ; all these contribute 

 to the possible risks to be guarded against. 



A somewhat novel and generally unsuspected 

 cause of petrol-fires is the power which the mobile 

 spirit has of generating static electricity. Ignition 

 of volatile oils through static discharge has been 

 known in hairdressers' shops, in garages where men 

 have chanced to clean their hands with silk rag 

 soaked in petrol, in filling up petrol tanks of motor 

 cars using a piece of chamois leather for filtration 

 purposes. A still more curious case is that of the 

 chauffeur who was drawing from a self-measuring 

 tank into a can bearing a wooden handle ; he hung 

 the can by this handle, thus insulating the receptacle, 

 and under these conditions the oil caught fire on two 

 successive occasions. 



The moral of these examples is obvious. They 

 serve to show, however, the meticulous care necessary 

 in handling petroleum under all conditions, and it 

 speaks volumes for the administrative and technical 

 ability of those responsible for storage and distribution 

 of oils, that the disasters attending oil-fires are so few, 

 not only in Great Britain but also in America, where 

 such vast quantities of inflammable spirit are dealt 

 with annually. H. B. Milner. 



The Greenwich Magnetic Observatory. 



Proposed Removal to Holmbury Hill. 



"jX/rAGNETIC observations were commenced at the 

 ^^'^ Royal Observatory, Greenwich, in the year 

 1840. They included absolute observations of the 

 magnetic elements together with eye-observations, 

 .obtained at first everj^ two hours and afterwards 

 fevery hour, for determination of the variation of the 

 elements. In 1847, continuous photographic records 

 |of the elements were introduced and have been con- 

 ftinued until the present time. The length of this 

 continuous series of observations provides valuable 

 material for the study of the phenomena of terrestrial 

 magnetism. It was by their means that Mr. Ellis 

 demonstrated the ii-year periodicity common to the 

 variations in the diurnal ranges of the magnetic 

 elements and to the sun-spot period, and that Mr. 

 Maunder established the connexion between the 

 recurrence of magnetic storms and the rotation of 

 the sun. More recently. Dr. Chapman, by using 

 the Greenwich observations, combined with similar 

 records of one or two other observatories which have 

 a long series, has been enabled to put forward a 

 comprehensive theory connecting magnetic storms 

 and the regular diurnal variations of the elements 

 with the electrification of and movements in the 

 atmosphere, caused by the discharge from the sun 

 of electrified corpuscles. The Admiralty magnetic 

 charts are constructed at Greenwich, the last issue 

 in 1922 consisting of three large-scale maps showing 

 the magnetic variation, and three smaller maps 

 showing the magnetic variation, dip, and horizontal 

 intensity for the whole world. 



During the last twenty years the magnetic observa- 

 tions have all been transferred to buildings con- 

 structed of non-magnetic materials in a special 

 enclosure in Greenwich Park away from the iron in 

 the Observatory. The instruments have also been 

 modified and improved. With the growth of electric 



traction in the latter part of the last century, steps 

 had to be taken to safeguard the Observatory from 

 disturbances due to leakage currents. Since 1903, a 

 protective clause has been inserted in all Parliarnentary 

 Bills for electric rail- or tramways running within five 

 miles of Greenwich, and a clause i"equiring insulated 

 returns if nmning within three miles. With these 

 safeguards, the disturbances, though perceptible, have 

 been kept within reasonable limits. 



On the decision of the South Eastern and Chatham 

 Railway Co. to electrify its local services which run 

 in the near vicinity of, and on both sides of, the 

 Observatory, the question of safeguarding the interests 

 of the Observatory was taken up with the Ministry 

 of Transport. It was ultimately agreed that the 

 most satisfactory arrangement for both parties, and 

 the cheapest for the railway company, would be to 

 move the magnetic observatory to another site, the 

 railway company defraying the costs of the removal 

 and the extra cost of maintenance thereby involved. 

 A site near London was desirable, not only so that 

 supervision from Greenwich would be easy, but also 

 in order to maintain a first-class magnetic station in 

 the south-east of England. After examination of all 

 sites within fifty miles of Greenwich which were at 

 least three miles from any existing railway, the region 

 which seemed to oi^er least probability of being 

 affected in the future by railway extensions or building 

 operations was that around Holmbury St. Mary in 

 Surrey. The site finally chosen as the most suitable 

 in the neighbourhood is on the lower slopes of Holm- 

 bury Hill. 



Some opposition has been aroused owing to it 

 being common land. The buildings to be erected on 

 it would be low and not unsightly, and would not 

 interfere with the amenities of the district. The fact 

 of being on common land would, on the other hand. 



NO. 2809, VOL. I 12] 



