Deg 9, 1881.J 



- KNOWLEDGE 



12i 



the stand and the quality of the lenses snppliod. This is very much 

 like an advertisement ; but yon, sir, may possibly know enough of 

 me to tell you that I am not an advertising agent. Anyhow, wherc- 

 ever the instrument is jiurchased, let " Twenty " see to it that he is 

 not misled by more apjiearance. Get a solid stand — one that won't 

 fhake and twist about ; and don't trouble about a lot of so-called 

 accessory apparatus. You won't want it. Then see that you have 

 a gooil inch and a good quarter-inch objective. You can do plenty 

 of work with them ; enough to make yourself a name in the world, 

 and get plenty of recreation too. I am the possessor of a £5 tele- 

 scope bought to let my bairns see the mountains in the moon, spots 

 on the sun, and something of Jupiter, Saturn, Ac. ; but shall I say 

 it, sir, and so shake your faith in my powers of replying to the 

 query, that is all the " astronomy " 1 have done with it. What it 

 does show it shows well, and enough for my purpose. That is all I 

 can say. — H. P. 11. 



[48] — Trisectio.v of Triangle. — There are three problems now 

 given up as beyond the power of Geometry, namely, (i) to trisect 

 any angle, (ii) to tind a straight line equal to the circumference of 

 a circle, and (iii) to find two mean proportionals between two given 

 straight lines. Thus, " Kuclid " is beyond the range of helji. — \V. G. 

 RoLFE. 



[54]— CiiEMKAL Q1EST10N.S.— The explanation of (1) is that the 

 iron of the ferrocyanide is not a base, but forms part of an acid, 

 which, however, has never been isolated. Potassium ferricyauide 

 acts in a similar way. A parallel case is chromate of potassium, or 

 any metal which will not ])recipitate, as hydrate, unless reduced by 

 zinc, or tin and acid. (2) To this part of "Castor and Pollux's" 

 (picry, I cannot see an answer, unless the solution were alkaline; 

 alkalies dissolving potassium tartrate. — C. T. B. 



[51] — Chemical Qiestioxs. — In the first case given by " Castor 

 and Pollu-x," the reason he has obtained no precipitate with ferro- 

 cyanide of potassium on adding the re-agents mentioned is this, 

 that he has been inattentive, I might even say careless, enough to 

 add hydrosnlphuric acid instead of ammonium sulphide. He very 

 correctly states that iron is one of the third group of metals, but 

 the metals of that group are precipitated by Am CI, Am HO and 

 Am HS, and not by U.S. And in the second case it is quite pos- 

 sible that the solution of tartaric acid was not sufficiently strong, 

 although the salts under examination may have been so. This test 

 is extremely delicate, and requires much more care than the ques- 

 tions of " Castor and Pollux" lead me to believe he has taken in 

 his analysis. — Theophilus Pitt, A.K.C. 



[55] — Greek Verbs. — Lengthening the vowel is the rule, devia- 

 tion from it the exception. Those verbs which retain the short 

 Towel take a in pf. and ppf-, med., or pass. ; also in their verbal 

 adjectives. — W. G. Bolfe. 



rSO] — Mercury's Revolctiox. — Undoubtedly 81 was a misprint ; 

 it should have been 88. — W. G. Rolfe. 



[00] — Sound being the effect produced on the car by any vibra- 

 tion, within limits of fastness and slowness, any substance that will 

 vibrate can transmit it. Tyndall compares ti-ansmission of sound 

 to a blow passed along a number of balls touching side by side ; the 

 last of the row only moves, so the last vibrated particle gives the 

 sound, and can pass it on from one substance to another. The 

 greater the elasticity — as steel, glass, ivory — and the lighter in 

 weight, the better does a body transmit sound. — C. T. B. 



[66] — Vexi's. — Tliis i)lanet is frequently visible in the day-time, 

 and often casts a shadow at night. — W. G. Rolfe. 



r66] — Vexus by Daylight. — Taking the above query of F. H. S. 

 to refer mainly to the planet's visibility in England, I may tell him 

 that, owing to the unfavourable atmospheric condition that generally 

 obtain here, she probably is not often visible during the daytime, 

 although I saw her plainly several times tliis summer, on different 

 days in (I expect) the month of July, when she had a considerable 

 north declination, and was at her extreme westerly elongiition from 

 the sun (or thereabouts). I should mention that by visibility I 

 mean visibility to the naked eye. If F. H. S. has sufficient know- 

 ledge of astronomy to understand the meaning of the terms " right 

 ascension " and " declination," he will know how to find the position 

 of Venus in the sky at any time by her bearing from the sun. 

 Abroad, within and without the tropics, I have seen Venus day after 

 day, for weeks at a stretch, and at sea have often determined the 

 latitude daily for like periods, both in the mornings from about 9 to 

 10, and in the afternoons from 2 to 3, according as she was, res- 

 pectively, to the west or to the east of the sun. In many of these 

 cases, however, she would not be visible to (he naked eye. If yotir 

 correspondent has not that slight skill in astronomy with which I 

 h&ve credited him, I am afraid yon would hardly allow me space to 

 explain to him how and when to " spot " Venus. — Winter. 



INFLUENCE OF MARRIAGE OX THE DEATH-RATE. 



[XoTE. — The enclosed is an answer to the query of " Bcnedioi " 

 upon the effects of marriage on -the death-rate, if you should 

 consider it worthy of insertion. — W. H. Peetwee.j* 



Foil several years it has been noticed by statisticians that the 

 death-rate of unmarried men is cousiderably higher than the death- 

 rate of nnirried men and widowers. 1 believe that Or. Stark, 

 Registrar-General for Scotland, was one of the first to call attention 

 to this peculiarity, as evidenced by the results of two years' returns 

 for Scotland. 



But the law has since been confinned by a far wider range of 

 statistical inquiry. The relative proportion between the death-ratci 

 of the married and of the unmarried is not absolutely uniform in 

 different countries, but it is fairly enough represented by the fol- 

 lowing table, which exhibits the mortality per thousand of married 

 and unmarrietl men in Scotland : — 



From this table we arc to understand that out of one hundreil 

 thousand married persons (including widowers), from 20 to 25 years 

 old, 026 die in the course of each year; w-hi!e, out of a similar 

 number of unmarried persons between the same ages, no less than 

 1,231 die in each year, .^.nd in like manner all the other lines 

 of the table are to be iutei'iircted. Commenting on the evidence 

 supplied by the above figures, Dr. Stark stated that " bachelorhood 

 is more destructive to life than the most unwholesome trades, or 

 than residence in an unwholesome house or district where there 

 has never been the most distant attempt at sanitary improvement 

 of any kind." And this view has been very generally accepted, 

 not only by the public, but Ijy professed statisticians; yet, as a 

 matter of fact, I believe that no such inferences can legi- 

 timately be drawn from the above table. If death strikes 

 do-wn in five years only half as many of those who are un- 

 married between the ago of 20 and 25 (as appears from 

 the above table), and if the proportion of deaths between 

 the two classes goes on continually diminishing in each suc- 

 cessive lustre (as is also shown by the above table), it seom.s 

 reasonable to infer that the death-i-ate would be even more strik- 

 ingly disproportionate for persons between the ages of fifteen and 

 twenty than for persons between the ages of twenty and twenty- 

 five. I believe, indeed, that if Dr. Stark had extended his table to 

 include the former ages, the result would have been such as I have 

 indicated. Yet few will suppose that very youthful marriages can 

 exercise so singularly beneficial an effect. It may appear at first 

 sight that we are bound to accept the conclusion that matrimony is 

 favourable to longevity. In the present instance we have simply to 

 deal with the fact that the death-rate of unmarried men is higher 

 than the death-rate of married men and widowers. All that we can 

 can do is to show that one of three conclusions must be adopted. 

 Either matrimony is favourable (directly or indirectly) to longe- 

 vity, in a degree sufficient wholly to account for the observed 

 peculiarity, on a principle of selection — the effect of which is such 

 as, on the whole, to fill the ranks of married men from among 

 the healthier and stronger portion of the community — operates in 

 a sufficient degree to account wholly for the observed death-rates ; 

 or, lastly, the observed death-rates are due to the combination, in 

 some unknown proportion, of the two causes just mentioned. No 

 reasonable doubt can exist, as it seems to us, that the third is the 

 true conclusion to be di-awn from the evidence supplied by the 

 mortality bills. Unfortunately, the conclusion thus deduced is 

 almost valueless, because we are left wholly in doubt as to the 

 proportion which subsists between the effects to be ascribed to the 

 two causes thus shown to be in operation. It scarcely required the 



• As I considered this article worth sending to the Daily News, 

 I suppose I may accept Mr. Pcrtwee's suggestion. Passages from 

 the article are quoted by Darwin, in his " Descent of Man," and his 

 approval led me to include the article in my " Light Science for 

 Leisure Hours." Mr. Portwee's quoting from the original suggests 

 that the matter may be new to many of our readers. — R. A. Proctor. 



