July 27, 1905] 



NA TURE 



307 



local practitioner who doriN'cd his livelihood by the good- 

 will of the local landlord ? 



Prof. Hewlett also denounced the way in which chemists 

 were taking upon themselves the bacteriological examin- 

 ation of pathological material, and emphatically asserted 

 that disease problems should be dealt with only by medical 

 men. He also advocated that a course of biology should 

 be obligatory for candidates for the associateship of the 

 Institute of Chemistry taking the subject of biological 

 chemistry. 



.^n interesting discussion, opened by Dr. Newman, of 

 Finsbury, was on the possibility of establishing a bacterio- 

 logical standard of purity of milk. Dr. Newman suggested 

 the following standards : — (a) not more than 24-25 degrees 

 of total acidity at the time of sale, i degree being equi- 

 valent to I c.c. of deci-normal NaOH solution ; (b) not 

 an excess of pus or blood ; (c) no B. coli, B. enteritidis, or 

 B. enteritidis sporogcucs ; [d) non-virulent to guinea-pigs. 

 All the speakers, including Dr. Allan Macfadyen, Prof. 

 Kenwood, Dr. Savage, Colonel Firth, Mr. Revis and 

 others, agreed that there was little possibility at present 

 of fixing a standard, and Dr. Newman's suggestions did 

 not obtain general acceptance. 



Another discussion, on the relative efficiency of chemical 

 and bacteriological methods for the examination of sewage 

 effluents, was opened by Mr. Dibden and by Dr. Savage. 

 There was a general agreement that chemical methods gave 

 a better indication of proper purification than bacterio- 

 logical ones, though, of course, bacteriological methods 

 alone were of service in detecting species of micro- 

 organisms. 



Lieut. Nesfield, I.M.S., gave an interesting demonstra- 

 tion of a method devised by him for the sterilisation of 

 drinking water during a campaign. He had found that 

 chlorine in the proportion of 2 grams per 100 gallons 

 acting for five minutes effectually destroyed the organisms 

 of cholera, typhoid, and dysentery. His method consisted 

 in carrying iron bottles of liquid chlorine, from which, by 

 means of a valve, the requisite amount was liberated into 

 the water. .After five minutes a powder of sodium sulphite 

 (2-2 grams) was added to the water, from which a double 

 decomposition ensued, and the water was rendered abso- 

 lutely tasteless. For the soldier on the march another 

 method was devised, so that he could sterilise for himself 

 a gallon of water. This consisted in adding to the vessel 

 of water a tablet containing iodide and iodate of sodium. 

 This resulted in the liberation of free iodine in the water, 

 which acted in five minutes as an efficient germicide, and 

 was then "killed" so that the water was rendered pot- 

 able, by the addition of another tablet of sodium sulphite. 

 In both processes the quantities of reagents employed are 

 so small as to have no effect on the human economy ; the 

 methods are rapid, and the reagents, Sec, portable. 



ECLIPSE SHADOW BANDS. 



/^\E of the most peculiar appearances attending a total 

 ^-^ eclipse of the sun is that generally known as the 

 " shadow bands." They are long dark bands, separated 

 by white spaces, which are seen on the ground or sides 

 of buildings just before and just after the total phase of 

 an eclipse, moving rapidly. It is probable that they are 

 not real bands, but are composed of dark patches which 

 seem to the eye to make long bands. Their cause is not 

 yet clearly known, as the observations in former eclipses 

 are quite discordant. The undersigned is very desirous of 

 obtaining observations of them at various stations along 

 the line of totality, especially at places near the edge of 

 the shadow, in order to compare with similar observations 

 made by himself and others. The observations require no 

 special instruments, and can be made by any careful 

 person. Information is desired upon the following 

 points : — (i) the direction in which the bands lie ; (2) the 

 direction in which they move ; (3) the velocity with which 

 they move ; (4) the width of the bands ; and (5) their 

 distance apart. All of these are likely to be different 

 before and after the total phase, so that two sets of 



NO. 1865, VOL. 72] 



observations are needed. The following suggestions are 

 compiled from various sources. 



Spread a white cloth or piece of canvas upon the ground 

 in any convenient open space. It is well to spread two 

 cloths or pieces of canvas, one to be used before, the other 

 after, the total phase. Let each observer be furnished 

 with several sticks, 4 feet to 6 feet long. 



About three minutes before the time of totality, let the 

 observer stand near the cloth with his back to the sun 

 and watch the cloth intently. If bands or dark patches 

 are seen, place one stick down in the direction in which 

 they lie ; after this is done place a second stick in the 

 direction in which they are moving. Both of these oper- 

 ations should be done deliberately, not hurriedly, and the 

 sticks left in position. 



During the total phase the observer is free to enjoy 

 the scene or make other observations, but it may be well 

 to note if any bands can be seen during totality, as some 

 have asserted. 



At the close of totality the observer should be at the 

 second cloth, or at another part of the single cloth (if he 

 uses but one), and should repeat the observations made 

 before totality, placing one stick down in the direction in 

 which the bands lie, and another in the direction in which 

 they ntove. 



It w-ill be seen that four sticks are needed for these 

 observations. If two persons make the records, one should 

 confine his attention to the direction in which the bands 

 lie, the other to the direction in which they move. The 

 bands are likely to be somewhat faint and poorly defined, 

 so that extreme accuracy may not be possible. 



The sticks should not be disturbed until after the eclipse, 

 when their direction should be determined with as much 

 care as possible, either by a compass or, still better, by 

 a surveyor's theodolite if one is available. If neither 

 compass nor theodolite is at hand, an estimate of the 

 directions should be made. 



The velocity with which the bands travel is more 

 difficult to determine. The estimates vary from the speed 

 of a man running to that of an express train. Several 

 methods may be suggested : — 



(i) Let two persons work together, one having a watch 

 with the seconds marked on the face. Let him mark time 

 by calling out each second. The number of the second is 

 not important, but a simple sound to mark the seconds 

 is suflficient. Let the other observer watch the bands and 

 see how many he can count per second. 



(2) With one observer marking time as before, let the 

 second observer note how many seconds elapse while a 

 band is passing between two objects the distance apart of 

 which is known. 



(3) Let a person run a short distance with the bands 

 and see if he can keep up with them. If not, let him 

 estimate how much faster the bands are moving than he 

 can run. 



(4) A mere guess at the speed is of some value. 



The width of the bands and their distance apart can 

 best be determined upon the cloths mentioned above, and 

 it will add to the accuracy of the estimates if the cloths 

 are divided by seams or in some other way into strips of 

 known width. A carpenter's rule will aid the observer in 

 making the estimates. The bands will probablv be several 

 inches wide and separated by spaces the width of which 

 is the same or greater. 



If the observer notices any other point connected with 

 the bands, such as their colour, whether they are straight 

 or wavy, whether they are continuous bands or made up 

 of dark patches, whether they flicker or not, the inform- 

 ation will be valuable. Still more valuable would be 

 photographs of the bands as they pass over the ground 

 or the side of a building or wall. 



It is earnestly requested that anyone who will kindlv 

 attempt the above, either in whole or in part, will send 

 his records to the undersigned. If for any reason the 

 observation seems unsatisfactory, either because the bands 

 were not as distinct as expected, or for any other reason, 

 or if the record is only fragmentary, it will still be of 

 value. The report should consist of a statement of the 

 methods employed by the observer or observers in making 

 the observations, and the results obtained, with anv 



