46 



SCIENTIFIC NEWS. 



[Jan. 13, 18 



of proficiency in physical science, will be awarded by means 

 of the examination for certificates to be held in July, 1888, 

 under the authority of the Oxford and Cambridge Schools 

 Examination Board. The exhibition will be tenable for three 

 years by a non-collegiate student of Cambridge or an un- 

 attached student of Oxford. Candidates must be non-colle- 

 giate students of one term's standing, or persons who have 

 not yet commenced residence at either University, and the 

 successful candidate must on election be admitted, if not 

 already admitted, and begin residence in the following 

 Michaelmas Term. Full information as to the subjects of 

 examination, the conditions of tenure of the exhibition, and 

 the preliminary steps to be taken by candidates may be 

 obtained from the Rev. F. G. Howard, M.A., the Censor of 

 Non-Collegiate Students, Cambridge. 



CORRESPONDENCE. 



The Editor does not hold hhnself responsible for opinions expressed 

 by his correspondents, nor can he take notice of anonymous com- 

 munications. All letters must be accompanied by the name and 

 address of the writer^ not necessarily for publication, but as a 

 guarantee of good faith. 



WATER SNAILS IN AN AQUARIUM. 

 I have an aquarium in which there are some water 

 snails, and I shall be glad if any of your correspondents will 

 explain to me how these snails manage to rise from the bottom 

 to the top of the water without apparent effort. It may be 

 that in some way they increase their volume when they wish 

 to rise, and that as their specific gravity is so near to that of 

 water, they then begin to float. Inquirer. 



THE EFFECT OF BAYONETS ON RIFLE FIRING. 



I saw it stated the other day in a north-country nev/s- 

 paper, that when a rifle is fired with the bayonet fixed a 

 deflection is caused in the flight of the bullet, and that this 

 deflection averages from 12 to 18 inches to the left at all 

 ranges up to 300 yards. I shall be glad to know if this has 

 been observed by any of your readers, and if so what is the 

 probable explanation of the occurrence. Militia. 



BRITISH SPECIES OF VIPER. 

 I find that a writer in one of your contemporaries 

 seeks to revive the view of our earlier naturalists, that we 

 have in Britain three distinct species of viper, viz., the com- 

 mon, the red, and the black. It seems to me that the black is 

 merely a local variety peculiar to mountains. Over the Con- 

 tinent the reptiles of such districts are of a darker colour than 

 their nearest representatives in the plains. The red viper I 

 should take to be the young female, which when mature 

 assumes more of a copper colour. R. M. N. 



A CURIOSITY IN CALCULATION. 



I was lately reading the article " Quaternions " in 

 the new edition of the "Encyclopaedia Britannica," and I 

 noticed that it bore the well-known initials of P. G. T. What 

 was my surprise, therefore, to find in it the following state- 

 ment : — In the case of time, measured from the Christian 

 era, this distinction is at once given by the letters a.d. or B.C., 

 prefixed to the date. And to find the position, in time, of 

 one event relatively to another, we have only to subtract the 

 date of the second (taking account of its sign) from that of 

 the first. Thus to find the battles of Marathon (490 B.C.), 

 and Waterloo (1815 a.d.), we have + 1S15 - ( -49o) = 2305 

 years ! " 



I would not have troubled you about this, but it strikes 

 me forcibly that Professor Tait has here, not only made 

 a slip, but has overlooked an important principle in 

 calculation. Without going into the minutiae of the altera- 



tion of the Calendar at different times, we are accustomed 

 in historical calculations to look upon all the years as of the 

 same length. To illustrate this more plainly. Suppose these 

 battles happened on the same day of the same month ; then 

 the number of years which intervene between these dates is 



NOT 2305. 



For let us consider the interval between the ist December 

 in the year i B.C., and the ist December in the year i a.d. 



M 



H 



N 



R 



Let N in this diagram represent the position in time of the 

 commencement of the Christian era, M N the year i B.C., 

 N T the year I a.d. ; for there no year o. Let H be the 

 position of the 1st of December in the year I B.C., and R the 

 position of the ist December in the year I a.d. What is the 

 interval between H and R ? Evidently only one year. That 

 is plain, by measurement, at the first glance. We have, then, 

 between the ist December in i B.C. and the ist December in 

 I A.D., the interval not of I - ( - i), or two years, but of one 

 year; that is one less than the sum of I and I. 



With the extension of the same reasoning, the interval 

 between, say, ist December, 490 B.C., and ist December, 

 181 5 A.D., is one less than the sumot these numbers, i.e., 2304 

 years. 



I shall be obliged for the opinion of any of your readers 

 on this subject. F. R. S. E. 



MEAN VELOCITY OF THE WIND. 

 Is there any positive evidence whether or no the climate of 

 England has become windier than it was some two or three 

 centuries ago ? I should incline to the affirmative view, on 

 two grounds : 1st, the prevalence in old directions for fore- 

 telling the weather, of the rule that it will be fair if smoke 

 ascends straight upwards, but that rain may be expected if 

 it falls. In our days smoke very rarely either rises or falls, 

 but is hurried along in a nearly horizontal direction from the 

 top of the chimney ; 2nd, that in the Book of Common 

 Prayer there is no form of supplication for deliverance from 

 destructive and unseasonable winds. — Cloud-gazer. 



— •-^»3>«^=«f-» — 



PUMPING BY ELECTRICITY. 



'X'HE pumps used for raising the water in mines are 

 generally driven by the pneumatic or hydraulic 

 power. The former requires a large initial outlay, 

 and the losses in transmission through horizontal pipes 

 for long distances are also considerable. The latter is 

 frequently a cheap and convenient way of transmitting 

 power if there be a sufficient head of water, but usually 

 an engine and accumulator are required on the surface, 

 and heavy piping must be provided. The great objec- 

 tion is that water has to be taken down the mine to raise 

 the water which is already there, and if the plant be 

 worked at high pressure, the cost of maintenance is con- 

 siderable. 



About four years ago Mr. W. B. Brain tried a pump 

 driven by electricity in a small colliery in the Forest of 

 Dean, and since then two other pumps have beem 

 started there. More recently Messrs. Immisch and 

 Co., of Kentish Town, have erected electrical pumping 

 apparatus at St. John's Colliery, near Normanton, which 

 has proved very successful. Wherever the requisite 

 power exists, it is only necessary to add a dynamo, a 

 motor, and conducting wires. The initial cost is then 

 about the same as for the pneumatic system; but the 

 cost of working is much in favour of electricity, as the 

 current can be so easily conducted to the place where it is 

 required without appreciable loss in efficiency. 



