620 



NATURE 



[February 3, 19 16 



star (Solasier papposus), of 8 to 9 cm. across their 

 extended arms, were placed in an aquarium at the 

 Horniman Museum at Forest Hill. The aquarium 

 already contained a whelk shell on which was an 

 average-sized "parasitic" sea-anemone {Sagartia para- 

 sitica). It should here be remarked that the sun-stars 

 were well fed daily (on pieces of fish, beef, mussel, or 

 starfish), and they could not therefore have been driven 

 by hunger to eat unaccustomed food. At 9.30 a.m. 

 on December 31 it was discovered that one of the 

 sun-stars was on the pebbles, humped in the char- 

 acteristic feeding posture over the sea-anemone, which 

 had apparently been dragged from the shell. Some 

 of the arms of the sun-star were raised and attached 

 by their tube-feet to the glass of the aquarium, and 

 the stomach of the asteroid could clearly be seen 

 enveloping about one-half of the coelenterate. Numer- 

 ous white acontia were attached to the under-parts of 

 the sun-star. At 10.30 a.m. on the following day the 

 sun-star was still upon the sea-anemone. The sea- 

 anemone was now removed from the aquarium, and it 

 was found on examination that the dead coelenterate 

 was closed, and that the integument of its upper parts, 

 together with" most of the tentacles,^ had disappeared, 

 having apparently been digested away. 



On January 13 another "parasitic" sea-anemone, 

 the diameter of whose circle of extended tentacles 

 was about 4 cm., was placed in the aquarium, and 

 at 9.30 a.m. oh January 15 it was found that it also 

 had been dragged from its shell and was enveloped by 

 a sun-star, which may or may not have been the same 

 individual. On this occasion the sun-star was not 

 disturbed in its meal. On January 17 it was still upon 

 the sea-anemone, but it had dragged its prey up a 

 vertical rock. When the sun-star was gently lifted, it 

 was found that the sea-anemone was inside the par- 

 tially everted stomach, only the central part of the 

 base of the coelenterate t)eing exposed. On the morn- 

 ing of January 18 (that is, at least seventy-two hours 

 after the attack) the sun-star was still humped a 

 little, and on its being turned over it was found that 

 there were no signs of the sea-anemone, except a 

 small dark-brown slimy mass, which the sun-star 

 hastily discharged from its mouth. 



The apparent indifference of the sun-star, with its 

 everted, and one would think vulnerable, stomach, 

 to the acontia is to be remarked. It would be of 

 interest to know whether any reader of Nature who 

 may be working^ at the asteroids has witnessed or 

 heard of an incident similar to those described above. 

 I may add that another average-sized "parasitic" sea- 

 anemone has been in the tank since the introduction of 

 the sun-stars, hut it has not yet been eaten, although 

 a sun-star will occasionally place itself over the 

 coelenterate and then creep away again. 



H. N. MiLLIGAN. 



Devonshire Road, Forest Hill, London, S.E., 

 January 29. 



William Smith's Maps. 



I AM preparing a monograph on Smith's maps, etc., 

 for the Yorkshire Geological Society, and am anxious 

 to see a " Reduction of Smith's large Geological Map 

 of England and Wales intended as an elementary map 

 for those commencing the study of Geology, 1819," 

 referred to in Phillips's "Memoirs of Smith." 



I find that Smith's large maps of 1815 often bear a 

 signature and a number such as "No. 66," or "a 33." 

 If any readers of Nature possess copies of this large 

 map perhaps they would kindly inform me what 

 number the map bears. It occurs under the " Section 

 of Strata," which appears on the map to the east of 

 the Humber estuary. T. Sheppard. 



The Museums, Hull, January 25. 



NO. 2414, VOL. 96] 



OPTICAL SIGHTS FOR RIFLES. 



OF all instruments needing- accurate pointings 

 the rifle has been longest deprived of the aid 

 of optical appliances. Probably this is due to a 

 variety of reasons, among them being : (i) the 

 roug-h usage to which a rifle may be subjected ; 

 (2) its use in warfare is essentially youth's pre- 

 rogative, with ample visual accommodation, so 

 that the disadvantage of open sig^hts is not acutely 

 felt; (3) the little incentive received from the use 

 of the shot gun with its spreading discharge, and 

 short range not demanding optical aid, as prac- 

 tice and judgment enter largely into the act of 

 aiming in much the same way as they do in 

 throwing a stone. Nevertheless, it is apparent 

 that the rifle is progressing through various phases 

 as other pointing instruments have done. 



The drawbacks of open sights are obvious- 

 — a near back-sight, a foresight, and a distant 

 object all require to be focused at the same time, 

 or rapid visual accommodation made (see Nature,, 

 June 24, p. 462). 



Optical sights for rifles may be divided intO' 

 three classes : (i) The use of lenses without 

 any tube, as in the early aerial telescopes, the 



Fig. I. — CoiniuoM's opU( al sight, sliov\ing 

 is made by Otiw:iy a ,d Co., 



rifle itself being used as a base on which the 

 lenses or lens and sighting hole are hidependently 

 mounted. (2) Use of lenses to give a reference 

 line, with or without other optical aid ; these are 

 termed coUimating sights. (3) Telescopes, pris- 

 matic or otherwise, complete in themselves with 

 optical or mechanical appliances for elevation or 

 deflection, and means for ready attachment to the 

 rifle. 



One of the earliest of class i is to be found 

 in a patent by Chase in 1893, i" which the fore- 

 sight consisted of a lens mounted near the muzzle 

 of the rifle, the focal length of the lens being such 

 that objects sighted at a distance had their 

 images in the same plane as the rear sight. This 

 image could be viewed either by the naked eye 

 or by optical means, and, of course, it appeared 

 inverted. Such an instrument has obvious dis- 

 advantages, but is capable of bringing all the 

 demands on the eye to a vision of one plane. 



Another single lens sight which is entirely 

 practical, and has achieved considerable success, 

 was patented by the late Dr. Common ii> 

 1901 and called by him "the optical rifle sight." 

 It consists of a lens mounted near the muzzle of 



