HARDWICKE'S SCIENCE-GOSSIP. 



65 



and antiquary, who has projected a photographic 

 survey of Warwickshire. The scheme is very elabo- 

 rately detailed, and is to include a topographical, 

 zoological, botanical, and geological survey of the 

 county by means of photography. We are evidently 

 on the lines of departure of a new system of geo- 

 graphical exploration. The degree to which amateur 

 photography and photo-micrography are extending 

 in this country is perfectly wonderful. A camera is 

 now as necessary to a gentleman's complete equip- 

 ment as a gold-headed cane was to our grandfathers. 



Mr. Isaac Roberts of Liverpool, the distin- 

 guished amateur astronomer, read a paper before the 

 Royal Society on a " Photographic Method for 

 Determining Variability in Stars." He showed that 

 photography could be better trusted than the human 

 eye, and he explained his method by which any 

 errors caused by atmospheric, actinic, or chemical 

 changes are eliminated, so that the study of stellar 

 variability can now be pursued under conditions 

 which admit of all necessary exactitude. Mr. Roberts' 

 method is to give two or more exposures of the same 

 photographic plate to a given sky space, with inter- 

 vals of days or weeks between each exposure. 



Mr. Brundenell Carter has recently read a 

 most valuable paper on "Vision-testing for Practical 

 Purposes." It has been proved that out of 125,127 

 persons examined, the percentage of those who were 

 colour-blind was 3*95. Mr. Carter strongly con- 

 demns the methods of testing for colour-blindness 

 employed on our English railways, and also by the 

 Board of Trade, declaring it to be not only quite 

 wrong, but the offspring of ignorance and presump- 

 tion, the very existence of which, he says, would be 

 incredible if the proofs of it were not daily brought 

 under our observation. 



Baron Nordenskiold, the intrepid and dis- 

 tinguished Arctic traveller and naturalist, whose 

 performance of the discovery of the north-east 

 passage in the "Vega " a few years ago is so well 

 known, has announced to the Swedish Academy of 

 Sciences, that he and another scientific cojifrlre 

 intend to start early next year on an expedition 

 to the South Polar regions. They announced that 

 they are being assisted in their contemplated work 

 "by the Australian colonies. 



A German scientist professes to have discovered 

 that electric currents are set up in the skin by mental 

 excitement. These can be detected by a delicate 

 galvanometer. Tickling sets up these microscopical 

 currents ; so does the sudden impact of hot or cold 

 water ; a needle prick, etc. Sound, light, taste, and 

 even smell will produce them. Nay, even the 

 indulgence of strong imagination can be thus 

 detected. It is a kind of electrical " thought 

 reading." Mental work will produce currents 

 varying with the amount. Thus the mental labour 



of a simple arithmetical sum hardly shows any 

 current, whilst the labouring out of a mathematical 

 problem sets them up intensely. If a person is in a 

 state of intense expectation, the mirror attached to 

 the galvanometer is in a state active oscillation. The 

 strength of these electric currents of the skin appears 

 to depend on the degree to which the part of the skin 

 bearing the electrodes is furnished with sweat-glands. 

 Thus some parts of the back, and of the upper leg 

 and arm (which possess comparatively few sweat- 

 glands) hardly produce any current. The scientist 

 above referred to considers that every kind of nerve 

 activity is accompanied by increased action of the 

 glands of the skin. It is already known that every 

 nerve function, causes a change of temperature, and 

 also the accumulation of the products of exchange of 

 material in the body. Increase of sweat production 

 helps to get rid of such products. 



The last new tip from South America, is the 

 discovery of a plant in the United States of Columbia 

 called Coriaria thymifolia, whose juices supply a 

 ready made ink, which is at first of a reddish brown 

 colour, but afterwards turns black. On this account 

 it has been called the " ink plant." 



MICROSCOPY. 



Philodina macrostvla, Ehr. ( = P. tuberculafa, 

 Gosse). — The dictum that all the known British 

 species of Bdelloida have three toes, which Dr. 

 Barnett Burns quotes, is not Gosse's, but Dr. 

 Hudson's, not being in brackets (see "The Roti- 

 fera," vol. i. p. 95, n. 2). But it is true that there 

 is a statement to the same effect as to the genus 

 Rotifer in Gosse's description of Actinurus. In 

 October, 1886, I received a letter from Mr. Gosse, 

 containing some information about this species, with 

 a drawing of the termination of the foot. In this 

 drawing only three toes are shown, but it is possible 

 that one of the inner toes may be hidden by one of 

 the outer. Mr. Gosse says, "the toes proper are 

 very seldom protruded." He states that the species 

 sometimes "occurs quite smooth, transparent, and 

 colourless," and then proceeds to describe the con- 

 dition figured in the Supplement. He adds that the 

 form of the spurs is very characteristic of the species. 

 The characters (or some of the characters) of P. 

 macrostyla were given in Pritchard's " Infusoria" as 

 long ago as ^845. Nothing is said as to the number 

 of toes in Pritchard's "Infusoria" (ed. 1845).— 7- W. 

 Blagg. 



New Boxes for Slides.— Mr. E. Mosely, of 

 Hastings, sends us one of his cleverly-constructed new 

 boxes for slides. The advantages will be apparent 

 from the annexed figure (Fig. 40)- By pulling out 

 the bottom drawer the others come out just far 

 enough to show the labels on the slides ; thus it will 

 be at once noticed if any one slide is missing. It 



