102 



SCIENTIFIC NE^A^S. 



[Feb. 3, 1888. 



The mixture is then placed in a special chamber where 

 the air is saturated with moisture. After a few days, 

 the colonies developed are counted by the help of a 

 magnifying glass. But to make the counting easier, the 

 glass -plate was divided into a number of equal squares 

 by the lateral scratches of a diamond. Mr. Blyth, with 

 the help of Mr. Archer, used an irgenious apparatus for 

 obtaining the water and its suspended particles at any 

 depth. And in the case of sewage the liquid had to be 

 diluted with distilled or sterilised water before being ex- 

 perimented upon, of course the mixing quantities being 

 duly marked. A convenient dilution is one of sewage 

 to a thousand of water. Drops of this diluted sewage, 

 added to the germinating gelatine, yield, after a few 

 days' cultivation, from 100 to 200 colonies. From the 

 calculation of the mixture, it was found by his observa- 

 tion of the colonies in the diluted sewage, that in June 

 the London sewage contained in a drop of the original 

 liquid no less than 160,000 colonies ; in July it contained 

 in a drop, three times that quantity ; and in November, 

 about half the quantity found in June. This shows 

 that the sewage is considerably influenced by season, 

 containing more in the summer than in the winter 

 season, but for the most part always yielding colonies 

 approaching to or above forty thousand per drop of 

 _se\yage. These colonies he found to be of all kinds of 

 fungi, more especially aspergilli, bacteria, bacilli, and 

 micrococci. 



Mr. Blyth examined several specimens of water, and 

 counted the germinated micro-organisms in a drop of 

 each specimen. A drop of water in a typical pond, 

 which received no drainage, but was frequented by ducks 

 and geese, contained 153 colonies, of which 20 were 

 bacilli and 2 were bacteria of the character Bacterium 

 termo. In an open well in Devonshire 400 colonies were 

 found in a drop of water. In the Regent's Canal, in its 

 course through London, he found very bad water, owing 

 to the stagnant character of the canal. A sample, taken 

 a foot below the surface, gave colonies equal to 1,400 

 per drop, whilst, just above the mud, another sample 

 gave 22,54«-colonies per drop. 



The water of a stream shows the same fact as in the 

 case of a stagnant pool or canal, that more micro- 

 organisms are near the bottom than near the surface. 

 For instance, Mr. Blyth found that the water of the 

 Thames j'ielded 500 colonies per drop near the surface, 

 and 2,750 colonies per drop close to the bottom. In the 

 same locality (at Sunbury) Mr. Blyth found in a second 

 sample, which was taken above some black mud, no less 

 than 280,000 colonies per drop. It thus appears that in 

 canals and rivers the bacteria slowly subside. 



In the sea-water round the coast of England the very 

 reverse is found as to the distribution of the micro- 

 organisms. In running and stagnant fresh water they 

 are much more numerous near the bottom, but in sea- 

 water they are more numerous near the surface. Samples 

 of sea-water, taken off the old pier at Brighton (in July), 

 were found by him to yield 730 colonies per drop on the 

 surface, and only 10 at the bottom. 



Mr. Blyth found that a public water supply, derived 

 from flowing rivers, or from any surface water, varies as 

 to its composition according to season, the more especially 

 as the water has a winter character due chiefly to winter 

 rains, and summer character due chiefly to the summer 

 drought. Month by month he analysed the water 

 supplied to London by the West Middlesex and Grand 

 Junction Companies ; and found that the colonies of 



micro-organisms per drop varied from 7 in May to 45 in 

 July, and down to 3 in November. This is far purer 

 than the water supplied to the city of Berlin, in which 

 140 micro-organisms are found in the drop in October 

 and 30 in February. 



Lake water he found to give a mean for nine months 

 of 20 organisms per drop, the greatest number being 

 observed in March and the lowest number in August. 



The conclusions to which Mr. Blyth has come after an 

 extended series of very careful observations are as 

 follows : — Sewage, pond and canal waters contain 

 enormous quantities of micro-organisms up to 180,000 

 per drop ; in canals and rivers the number of these 

 organisms is greater near the bottom than near the 

 surface ; in sea water the number of organisms is greater 

 near the surface than near the bottom ; and a good 

 water should not contain more than 40 micro-organisms 

 per drop, when cultivated within 24 hours after 

 collection. 



— ♦^;»t^^5<^* — 



CHARACTERISTIC EFFECTS OF DYNA- 

 MITE AND GUNPOWDER. 



PROFESSOR TAIT has lately pointed out to the 

 members of the Royal Society of Edinburgh the 

 effects of the explosives, dynamite and gunpowder. 

 Many of the victims of the explosion by dynamite in the 

 London Underground Railway', the other year, are 

 reported to have entirely lost the sense of hearing in the 

 side of the head which was next the source of the explo- 

 sion. This is a curious fact. The result points to a 

 direct projectile motion of the air and of the gases pro- 

 duced by the explosion, instead of the ordinary wave 

 motion. The disturbance must travel far faster than 

 sound ; for the ordinary undulatory motion would not so 

 injure the drum of the ear. 



This intensely powerful projectile motion is witnessed 

 in the case of forked hghtning. Here the air seems to be 

 driven outwards from the track of the discharge with 

 such speed as to render the immediately surrounding air 

 instantaneously self-luminous by compression. Moreover 

 this theory bears out the photographic result which 

 cannot be accounted for by ordinary irradiation. For the 

 forked lightning flash is always photographed as a line of 

 finite breadth, even when the focal length is short 

 and the focal adjustment is perfect. 



According to Professor Tait these considerations show 

 at once how to explain the diiference between the effects 

 of dynamite and those of gunpowder. The latter is pre- 

 pared expressly for the purpose of developing its energy 

 gradually, superficially, and in an upward direction. 

 Thus, while the flash of gunpowder fired in the open air 

 is due mainly to combustion of scattered particles, that 

 produced by dynamite is mainly due to impulsive com- 

 pression of the immediately surrounding air, energy be- 

 ing conveyed to it much faster than it can escape in the 

 form of sound. The energy of the dynamite is not 

 exercised so gradually as with gunpowder ; it is sudden, 

 acting in all directions, downwards as well as upwards, 

 defying all the limiting superintendence of the wave 

 phenomena. 



Earthqu.^kes. — On the 8th ult. a shock was felt over 

 a great portion of Algeria. On the 12th shocks were 

 felt at Columbia, Charleston, and Summerville, in 

 America. 



