Jan. I o, 1878] 



NA TURE 



215 



precedes the jump of the true spark is extremely feeble, in com- 

 parison with that which takes place after the spark has passed 

 and the voltaic arc has formed ; even when the point and disc are 

 not more distant than '02 inch beyond the striking distance 0-34 

 inch for 8,040 elements, it is only ^-jWh part of it. 



The appearance of the discharge is very different, according 

 as the point is positive or negative ; it is interniittent in both 

 cases, but is much less discontinuous when the point is negative 

 than when it is positive, as can be seen with a microscope having 

 a rotating minor p'aced in the btnd of the body between the 

 objective and eye-piece. The appearances observed are shown 

 in the wood engravings which illustrate the paper. 



Between a point and a disc the spark is longest with the point 

 positive, when from 5,000 to 8,000 cells are used ; but for a less 

 number of elements, 1,000 to 3,000, it is longest when the point 

 is negative. 



The length of the spark is greatly influenced by the form of the 

 point ; thus with a point in the form of a cone of 20 degrees the 

 striking distance is o"l84 inch with 5,640 cells, and 0'267 

 inches with 8,040, while with a point approaching a paraboloid 

 in form, and with the same base and of the same height as the 

 cone, it is 0-237 i"ch with 5,640 cells, and 0343 inch with 

 8,040. 



The striking distance between a point and a plate is in accord- 

 ance, very nearly with the hypothesis of this distance, increasing 

 in the direct ratio of the square of the number of elements, at all 

 events up to 8,040 cells, thus ^ : — 



Number of cells ... 1,000 2,coo 3,000 4,000 5,000 6,000 7,000 8,000 



in. in. in. in. in. iti. in. in. 



Distance obferved ... o'oosi o'o22i o;os54 0*103 o'isp o'222 o'286 o'352 



Distance calculated... 00055 00220 0^0495 o*o88 o"i375 o'jgS 0*2695 0352 



Between plane, spherical, or cylindrical surfaces, the striking 

 distance does not follow this law ; on the contrary, the increase 

 is nearly, but not quite, in the ratio of the number of cells. 



1,000 cells. 8,000 cells. 



Between spherical surfaces 

 Plane ,, „ 



Two concentric cylinders 



0*0050 

 0*0104 

 00071 



o*o8io 

 o 0852 

 0*099 1 



The striking distance between two"paraboloidal 'points Was 

 found to be with— 



1,080 cells. 



in. 



0*005 



8,040 cells. 



in. 



0*401 



The nature of the metal used for terminals has, in almost all 

 cases, no influence on the length of the spark, but there is one 

 striking exception, namely, in the case of aluminium ; when an 

 aluminium point is used the spark is longer than with points of 

 all other metals tried, in the ratio of 1*242 to i.j 



The length of the spark is different in various gases; for 

 example, air, oxygen, nitrogen, hydrogen, and carbonic acid, 

 and the ratio between the lengths of spark in various gases varies 

 with the forms of the terminals. The length of the spark bears 

 no simple relation cither to the density of the gas or its viscosity. " 



The paper contains an account of a few experiments on the 

 length of spark in air at different pressures, from 141*5 millims. 

 to 760 millims. Between a point and a disk the length of the 

 spark increases nearly, but not quite, in the ratio of the dilata- 

 tion ; but between two spherical surfaces it increases far more 

 rapidly, and it is possible that at a certain degree of rarefaction 

 the striking distance may be coincident for spherical surfaces and 

 points. 



When a strong resistance is interposed in the circuit, 4,000,000 

 ohms for example, the discharge is completely changed in 

 character ; instead of the ordinary spark and production of the 

 voltaic arc, very brilliant snapping sparks pass between the 

 terminals at more or less rapid mtervals, exactly like the sparks 

 of a small Leyden jar. Then pierce a piece of writing with 

 minute holes. 



It has been found that an accumulated charge of a condenser 

 of 42*8 microfarads capacity, charged with the potential of 3240 

 cells, produced neither an elongation nor a contraction of a 

 metallic rod 02 inch when suddenly discharged through. This 

 charge deflagrates 10*5 inches of platinum wire 0*0125 inch in 

 diameter. 



More dense sparks were obtained with one of App's coils for 

 producing 6-inch sparks when the primary was connected with 

 1080, 2280, 3480 chloride of silver cells, than when it was used 



• Proc, Roy. Sec, 1876, vol. xxiv. p. 167. 

 ' Proe, Roy, Sac , vol. xxvi( p. 227. 



ftUHHl J." 



with a zinc-carbon,T bichromate of potash battery of six cells 

 producing a current 300 times as great, thus showing the in- 

 fluence of high potentials in inducing secondary currents. 



These currents of high potentials have also a marked effect in 

 inducing magnetism, when the actual current is taken into 

 account. 



The second part of the paper, which is in coarse of preparation, 

 will deal with the discharge in rarefied gases, in the so-called 

 vacuum tubes. 



Chemical Society, December 20, 1877. — Dr. Gladstone, 

 president, in the chair. —The following papers were read : — On 

 the constitution of the terpenes and of camphor, by Dr. Arm- 

 strong. — Communications from the laboratory of the London 

 Ini-ti'ution, by Dr. Armstrong. — On the hydrocarbons from 

 rinus sylvestris, with remarks on the constitution of the terpenes, 

 by Dr. Tilden. The author has examined the terpeaes from 

 Russian turpentine oil and Olnim fo'.iorum pint sylvestris. He 

 considers that there are probably only three isomerides amongst 

 the natural terpenes, and suggests a formula for these bodie< 

 derived from that of diamylene. — On citric acid as a constituent 

 of imperfectly ripe mulberry juice, by Dr. Wright and Mr. 

 Paterson. This juice was found to contain 26*83 g'^'^- of citric 

 acid and 3*26 grm. of potash salts per litre; the authors point 

 out that it may be valuable as an antiscorbutic, and as a substitute 

 for lime juice. — On cuprous chloride and the absorption of car- 

 bonic oxide and hydrochloric acid gas, by J. W. Thomas. The 

 author suggests a ready method of making a solution of cuproas 

 chloride for gas analysis, but finds that although a solution of 

 this salt absorbs carbonic oxide readily, sixty-three per cent, of the 

 gas may be again liberated on neutralising the solution with 

 potash. To avoid such an error he just neutralises the solution 

 of cuprous chloride with ammonia and in this way prepares a 

 solution which introduces into the absorption tube neither free 

 ammonia nor free acid, but which absorbs carbonic oxide with 

 facility. The author has also observed that a saturated solution 

 of ammonic sulphate absorbs hydrochloric acid gas with great 

 readiness, forming an acid salt and ammonic chloride. 



Anthropological Institute, December 11, 1877. — Dr. John 

 Evans, D.C.L., F.R.S., president, in the chair. — Dr. James F. N. 

 Wise was elected a member. — Mr. Worthington Smith exhibited 

 some objects from Maiden Bower, and a series of camera lucida 

 drawings of several stone monuments in Wales. — Mr. A. Jukes 

 Browne, F.G.S., exhibited a series of flint flakes, scrapers, and 

 arrow points from Egypt, and read an interesting paper on the 

 subject. He described the geological formation of the country 

 round Helwan about sixteen miles south of Cairo, whence the 

 flints were obtained, and explained the denuding action of the 

 Nile in this locality. He thought that the finding of separate 

 implements in each site pointed to there having been flint manu- 

 factories on those spots which, moreover, were near the hot 

 springs. No adzes or celts were found, but fragments of horses' 

 teeth split into long pieces were among the flints. The flintj 

 used in the manufacture of these implements were pebbles found 

 on the lower plateau which had been washed down from the hills 

 of eocene limestone above, the upper beds of which abound in 

 siliceous concretions of various sizes. — Mr. Jukes Browne als i 

 exhibited some flint implements from a site on the borders of the 

 Fens in Lincolnshire, which appeared to have been a station or 

 manufactory similar to those at Helwan. The president and Mr. 

 Moggeridge made some remarks on the above. — Mr. J. Park 

 Harrison communicated a further report on the "cave-pits " at 

 Cissbury. He said that the galleries belonging to it, and the 

 pits adjoining, appeared to have been used as places of shelter 

 and concealment for some considerable time after they were 

 excavated. No evidence existed at present that they were 

 habitations. One shaft, to which there was access from the cave- 

 pits, was found to have been left unfinished with the horn tools 

 lying where the work had been interrupted. Several small oval 

 pits, the largest only 5 feet long, and 4 feet 6 inches dtep, were 

 met with this autumn for the first time in the neighbourhood of 

 the shafts. Among their contents were sling stones and small 

 pieces of flint and fractured rubbing-stone bearing marks of fire, 

 fragments of pottery of various dates, a few flint implements 

 and many flakes ; also three weights formed of chalk (similar to 

 some found in Mr. Tindale's pit) ; a carding-comb, a small iron 

 hook, and three pieces of burnt clay with the impress of sticks 

 on wattles. A few bones of calf, roebuck, pig, and goat, with 

 two or three shells, were the only animal remains. They would 

 appear to have been preserved by the charcoal and chaired 

 matter in ' cdntact With' them. If the little pits were graves 



