4H 



SCIENTIFIC NEWS. 



[Nov. 9, 1888. 



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. 



THE SPARROW AGAIN. 



Beginning at the end of the very positive letter of your 

 correspondent, Mr. J. P. Nunn, I must inform him that I used 

 the word " swallow " generically for the entire genus Hirundo. 

 Their taking possession of a martin's nest is of such constant 

 occurrence that I have known the latter birds to be positively 

 driven away from a gentleman's mansion in Essex, in spite of 

 all efforts for their protection. Their persecution of the true 

 insectivorous birds is a sad reality. A correspondent of the 

 American Naturalist describes the repeated raids which they 

 made upon a wren's nest in his garden, and how he was 

 obliged to protect the nest with a cover having a hole too 

 small for the sparrow to enter. Now, as the wren is one of 

 our most diligent insect-eating birds, this is a case in point. 

 Further observations, alike in America and Europe, go to show 

 that in proportion as the sparrow multiplies in any district 

 other small birds become scarcer. 



The suggestion that I "cannot know what kind of bird the 

 American robin is," is very wide of the mark. I knew it forty 

 years ago. But the comparative size of the birds is quite 

 beside the question. If on opening the crops of two birds we 

 find that of the one mainly filled with insects and that of the 

 other with grain and fruits, we know at once that the former 

 is a friend to the farmer and gardener, and the latter an enemy. 



I am perfectly aware that the swallows do not feed on grubs 

 and caterpillars. But I would invert Mr. Nunn's exclamation, 

 and say, " If the flies and the moths are to be allowed to live 

 and deposit their eggs that these may turn into food for 

 sparrows, woe to all our fruits and flowers ! " Sparrows, 

 thinks Mr. Nunn, " congregate where they can obtain food." 

 So do other birds. His examination of the nests of eighty- 

 nine pairs of sparrows proves nothing, unless he can also 

 show how many broods a pair of sparrows may have in a 

 year (whilst many other species have one only), and how 

 many nests there are, say, per square mile, and then make a 

 comparative census of the small birds in the same manner. 

 Until he has done this he has proved nothing. 



The observations of S. A. Forbes are perfectly conclusive, 

 at least for the district where they were made. Let Mr. 

 Nunn shoot a few of his clients, and make an examination of 

 the contents of their stomachs, and he will, I believe, find him- 

 self compelled to throw up his brief. Aruspex. 



THE COCHINEAL INSECT. 



The writer of the article on " Cochineal Insects " (Scientific 

 News, p. 459) can scarcely be aware that the dye obtained 

 from these insects, once so valuable, is rapidly falling into 

 disuse, being to a great extent superseded by the azo-scarlets 

 obtained from coal-tar. In consequence, many of the Coccus 

 gardens are being turned to other uses. 



The " green dye " obtained from caterpillars has been 

 proved by Mr. Poulton and others to be identical with the 

 chlorophyll or leaf-green of plants, and if required for use in 

 the arts can be much more readily obtained from grass than 

 from spinach. A Tinctorial Chemist. 



DRAGON-FLIES. 



Will you allow me to inform your numerous readers 

 interested in entomology, that I shall be very pleased to assist 

 any one desiring to commence the study of dragon-flies 

 (Odonatd). I shall also be glad to name and identify any 

 specimens of these grand insects which may be sent to me. 



Birmingham. W. Harcourt Bath. 



ANSWERS TO CORRESPONDENTS. 

 Teignmouth. — The subject of your communication was 

 dealt with on page 193 of vol. i. of the Scientific 

 News. We would direct your attention to the rules at 

 the head of this column. 



RECENT INVENTIONS. 



The folloiving list has been compiled especially for the Scientific 

 News by Messrs. W. P. Thompson and Boult, Patent Agents, of 

 234, High Holborn, London, W. C. ; Newcastle Chambers, Angel 

 Row, Nottingham ; Dude Buildings, Bank Street, Manchester ; 

 and 6, Lord Street, Liverpool. 



Propeller for Vessels. — Mr. R. Morris has patented- 

 a means for propelling vessels, torpedoes, etc., by com- 

 pressed air. A cylinder is provided and fitted with a 

 plunger, piston rod, and an air valve at each end. When 

 the plunger is put in motion air is taken into the 

 cylinder through the valve at one end and is forced out 

 through the other valve into a pipe which passes through 

 the exterior of the vessel to the water outside. The 

 compressed air is thus forced against the water and suffi- 

 cient force obtained to propel the vessel. 



Galvanic Batteries. — Mr. P. Skrivanow has patented 

 a galvanic battery. This battery consists of an electrode 

 of iron, and a plate of retort charcoal. Over the latter 

 is spread a layer of peroxide of lead, and the whole is 

 enveloped in a sheet of parchment paper retained by 

 rubber bands. The two electrodes are placed in a 

 solution of hydrate of potassium. A dry battery can be 

 obtained by covering the positive electrode with several 

 sheets of filtering paper soaked in the above solution, 

 and applying above it the negative electrode. 



Marine Engines. — Mr. J. McGregor has patented a 

 compound marine steam-engine so that the steam may 

 be expanded through three successive stages with a 

 satisfactory distribution of the various strains. To carry 

 out the invention four cylinders are used in each in- 

 stance, connected by pairs to two cranks on the same crank 

 shaft. In a modification two high-pressure cylinders are 

 geared to and work at the back of an intermediate and 

 a low-pressure cylinder, the valves of the high pressure 

 cylinders being actuated by an extension of the valve 

 rods of the two larger cylinders. 



Electric Shocks. — Messrs. J. Douglas and H. Abbott 

 have patented an apparatus for producing and adminis- 

 tering electric shocks. A case is provided containing a 

 tray for carrying the battery, suspended by cords from a 

 cross-bar fixed to two telescopic tubes which form 

 handles outside the case. The pulling out of the tubes 

 over their cores carries the cross-bar with them, and at 

 the same time the tray and battery are lifted. The cross- 

 bar carries a bracket to which the core of a magnet is 

 fixed, so that as the handles are drawn out the current is 

 increased. The weight of the tray and battery takes 

 back the handles when released. 



Watch. — An improved watch or chronograph has been 

 patented by Messrs. H. and C Turler, of Bienne, 

 Switzerland, the object of which is to enable the wearer 

 to ascertain any space of time which has elapsed during 

 a given period. In addition to the ordinary hands, the 

 watch has three smaller supplementary dials, each pro- 

 vided with mechanism which is thrown into operation 

 when desired, and on which are recorded the hours, 

 minutes, and seconds respectively which have elapsed 

 during the time it is desired to measure. When the 

 special dials are not required, the mechanism is thrown 

 out of action, and the watch is similar to an ordinary one. 



Electro Motors, — Mr. M. Immisch has patented an 



