;74 



SCIENTIFIC NEWTS. 



[Oct. 5, if 



CORRESPONDENCE. 



The Editor does not hold himself responsible for opinions expressed 

 by his correspondents, nor can hetake 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. 



A SAFE INSECTICIDE. 



Referring to the notice in your columns of to-day of the 

 application of sulphate of copper as an insecticide, it is stated 

 in the first Annual Report on the injurious and other insects of 

 the State of New York, by J. A. Lintner, the State entomo- 

 logist, that " Sprinkling with a weak solution of blue vitriol, 

 one ounce to a pail of water, kills many kinds of larvae." In 

 the exhaustive account which is given in this volume of the 

 remedies for insect depredations known in the United States, 

 the safety of the application is regarded ; and virulent poisons, 

 such as blue vitriol, require extreme caution in their manipu- 

 lation. 



The sulphate of iron, which is probably the most fatal of 

 any chemical to the smaller forms of insects, is so harmless 

 to human life that five grains are given as a dose, and minnows 

 are unaffected by a solution of eight grains of this sulphate in 

 a gallon of water. Vol. xiii. of the Professional Papers of 

 the Corps of Royal Engineers, contains an account of the 

 destruction of aphides, micro-organisms, and those more 

 recently discovered forms of life to which the phenomena of 

 putrefaction are now attributed, by a very weak solution of 

 iron ; and where the destructive enemies of plant life are too 

 large to be thus rapidly destroyed, the solution still acts as 

 an andidote to their attacks, as few, if any, insects will 

 approach a vegetable that has been watered with a solution 

 of iron. 



The simplest mode of obtaining a stable solution of iron 

 for the use of the garden or greenhouse is to draw it off 

 from the cup of the ferrometer. This is an instrument for 

 household purification, which is described in the professional 

 paper cited. It is manufactured by Messrs. Filmer and 

 Mason, of Guildford ; is now in use at Windsor Castle, 

 Buckingham Palace, Hatfield House, Albury Park, and a 

 number of other places. The perfect sweetness of the dwelling- 

 house is the main result of the use of the instrument ; but 

 the subsidiary value for the garden and greenhouse is not to 

 be despised. Francis R. Conder, M. Inst. C.E. 



Guildford, Sept. 22nd, 1888. 



STRANGE ACTION OF A BEETLE. 

 " I was amused at reading of the beetle's strange conduct, 

 for I happened to be acquainted with a man of science who 

 acts exactly in the same way. He goes round and round so 

 many times a certain piece of ground to take a constitutional, 

 and when he lias accomplished a certain number of rounds he 

 knows that he has walked a certain number of miles. The 

 one eye idea (see Scientific News Sept. 7th) I should hardly 

 think sufficient to account for it, but in Nature I remember 

 reading some account of an American experiment in walking 

 blindfold. Often people have one leg a little shorter than the 

 other, and in this case the tendency is to walk when blind- 

 folded, in the direction of the shorter leg. 



The beetle's strange conduct mig/it have something to do 

 with this, but I do not think so. It is probable that insects 

 are much more intelligent than we generally suppose them to 

 be A Reader. 



THE SATELLITES OF MARS. 

 There is a paragraph in your journal for September 14th, 

 page 279, in which the theory of M. Dubois is mentioned, 

 but I think there are very few astronomers who will give it 

 their adhesion. The satellites of Mars, instead of being 

 captured planetoids, very probably date their origin from a 

 period coeval with their primary. This conclusion is upheld 

 by the analogies of the solar system. Bode's law of planetary 

 distances is, we know, exemplified in a remarkable manner, 

 an'i there also appears a definite law in regard to the numbe r 



of satellites. They increase, in duple proportion, according to 

 their distance from the sun thus : 



Earth. 

 1 



Mars. 

 2 



Saturn. 



Jupiter. 



4 8 



Uranus and Neptune would probably further bear out this 

 law, could we view them with greatly increased telescopic 

 power, for the known satellites of these remote members of 

 our system form but a small proportion of the whole number 

 of satellites which belong to them. It is probable that 

 Uranus has 16 and Neptune 32 satellites. We are justified 

 in this assumption by the regular increase in the number of 

 moons attending Mars, Jupiter, and Saturn, which is very 

 likely to be extended to the two outer planets of the system. 

 We are probably cognisant of all the satellites revolving round 

 the earth, Mars, Jupiter, and Saturn, but the immense dis- 

 tances of Uranus and Neptune preclude us from discovering 

 any but the most brilliant of their satellites. These bodies 

 were evolved or formed as the result of a comprehensive and 

 harmonious scheme, and we are not driven to such an erratic 

 inference that the moons of any of the major planets are due 

 to the capture of planetoids. 

 A Member of the Liverpool Astronomical Society. 



FOOD OF THE LEECH. 



Can any of your readers inform me of the general food of the 

 common leech ? In the ponds which it inhabits it seldom 

 has the opportunity of feasting on blood, and it does not 

 readily attach itself to the skin even when laid on the hand. 



Perhaps leeches feed on aquatic plants, as they are often to 

 be found adhering to the stalks of weeds, such as Alnacharis 

 alsinastrum. I do not think they ever attach themselves to 

 fishes, as I have sometimes placed sticklebacks in with them 

 without their attempting to fasten. I have never noticed 

 any allusion to their food (when living in ponds) in any book, 

 and should be pleased to know the real facts of the case. 



F. P. P. 



THE SPARROW (Passer domestic™). 



In my notes made in 1886 I stated that the large quantity 

 of fine dust found in the nest of the sparrow was not acci- 

 dental, but placed there intentionally ; this appears to be the 

 fact, for I have seen the sparrow collecting the fine dust from 

 the road on pieces of material for building. 



By way of leading up to what I am going to say, I may 

 again state that in 1886 1 found from 20 to 25 per cent, of in- 

 fertile eggs, and in 1887 about 30 per cent. ; but in the season 

 of 1888 just passed I found the percentage of infertile eggs 

 considerably reduced, and also a very considerable reduction 

 in the number laid, the average clutch being four eggs, 

 whereas in 1887 it was four and a half eggs. I stated in my 

 paper last year that the eggs laid in 1887 were not so highly 

 coloured as those of the previous year, and the infertility 

 greater ; but when I made this statement I little thought that 

 colour and fertility were intimately connected ; nevertheless it 

 appears to be the case, for the eggs of the season just past, 

 of which I have ninety perfect clutches before me, are most 

 certainly of a darker colour than those of the previous year. 

 I may here state that the odd egg in the clutches just referred 

 to is not so pronounced as it is in the clutches of the two 

 previous years, and its infertility was not greater than an}' of 

 the eggs of the ordinary type. This accounts for the fact that, 

 as a rule, the more pronounced the odd egg the greater its in- 

 fertility, and that in the two previous years the clutches bring 

 one half egg larger and of a lighter colour, and with a more 

 conspicuous odd egg, proves that what I said as to the high 

 percentage of infertility in the odd egg about correct. 



The discrepancy between eggs and brood of the season just 

 passed appears to have been about l6i per cent., the average 

 clutch being four eggs, and the average brood three and one- 

 third young birds, against three and one-eighth last year. 

 The general discrepancy is not altogether brought about by 

 the actual sterility of the eggs, but by many of them produc- 

 ing only a weak young bird, which either died in the nest or 

 was turned out to die. Tlr's is a fact about which there can 



