April 1, 1868.] 



HARDWICKE'S SCIENCE-GOSSIP. 



93 



Insects never Grow. — The mealy bug (Coccus 

 Sp), numerous species of aphis, and the females 

 of termites grow prodigiously after they have 

 attained their full development as imagos ; not 

 so grasshoppers, locusts, &c, although they do so in 

 the earlier stage. But as in these insects the stages 

 are less clearly defined to the eye than in 

 Coleoptera or Lepidoptera, the superficial observer 

 might easily imagine that they grew in all stages. 

 The same may be said with the aphis and blatta, or 

 cockroach families. Female moths and flies, if they 

 do not increase in length, do so greatly in girth, 

 after they attain the perfect state. — C. 0. G. Napier, 

 F.G.S. 



Chrysalis in Rock. — In Science-Gossip for last 

 October I gave an account of a chrysalis found in a 

 piece of rock under rather strange circumstances, 

 promising if the imago ever appeared to inform you 

 of it. On Saturday last, by chance I opened the 

 box. where it was placed, and, to my astonishment, 

 saw an insect rapidly running to and fro. It had 

 but just emerged from the pupa case, as the wings 

 were not developed until an hour later. The insect, 

 which at first sight much resembles the common 

 housefly, is quite new to me, but doubtless is well 

 known to entomologists. It belongs to the Diptera. 

 The eyes are prominent, antennae and palpi short ; 

 the thorax is broad (same width as head) ; the 

 abdomen narrow and hairy; tibiae also hairy, with 

 rows of strong bristles ; the tarsi have five distinct 

 articulations, terminated by two claws. — M. Pope, 

 Weymouth. 



Expansive Power. — In reply to your correspon- 

 dent, Edwin Holmes, allow me to inform him that 

 the facts which he states in his quotations from an 

 article on the " Temperature of Lakes " are entirely 

 incorrect. Water contracts during the process of 

 cooling only until it reaches + 4° centigrade ; it then 

 expands, instead of contracting, for any further loss 

 of temperature ; until it reaches 0° O, when it 

 assumes the solid form, and in so doing undergoes a 

 further expansion. Let us now see how that which 

 I have stated above applies to the economy of lakes 

 and seas. Imagine a large body of water the surface 

 of which is exposed to the atmosphere. If, now, the 

 temperature of the atmosphere falls, the layer of 

 water in contact with the superincumbent air 

 becomes denser and of greater specific gravity, and 

 therefore sinks. This continues until the tempera- 

 ture of the whole mass of water reaches + 4° 

 centigrade ; then, as it becomes colder, instead of 

 the surface-layer contracting, it expands, becomes 

 lighter, and therefore remains at the top, while the 

 whole of the water underneath never falls below 

 + 4° C. Now what would have taken place were it 

 not for this peculiar property of water ? The upper 

 layer of water would have continued to become 

 colder and denser, and consequently to sink until 

 the whole mass attained the temperature of 0° C, 

 when upon the slightest further decrease of tem- 

 perature the whole mass would become solid. — 

 /. /. /. 



White's Hybrid Pheasant.— In my copy of 

 " White's Selborne," by Capt. Brown, there is a 

 note by the Captain as follows: — "This curious 

 lusus naturee is now in the collection of the Earl of 

 Egremont, at his seat at Petworth, and is allowed 

 by naturalists to be a mule between the blackcock 

 and common pheasant," p. 292.— C. 0. G. Napier, 

 F. G. S. 



Medium.— Will any of your correspondents kindly 

 answer the following queries ? What is that medium 

 mentioned by Mr. Millar in a short paper on 

 " Mounting Insects " in the addenda to " Hogg's 

 History of the Microscope " (fifth edit.), as having, 

 he believes, been discovered by the Rev. J. Thornton, 

 which will destroy the animal tissues, soften the 

 chitine, and combine with turpentine — potassse and 

 acetic acid (the solvents commonly used) being so 

 inconvenient in consequence of producing milkiness, 

 and thereby destroying the insect unless very care- 

 fully soaked in turpentine ? — /. W. G., 25, Charlotte 

 Street, Bedford Square. 



Cromlechs.— I don't think it likely that Mr. 

 Allen would consider the Welsh cromlechs had 

 ever been the habitation of a race of giants. They 

 certainly far more resemble in character sepulchral 

 monuments, and it is more than probable that the 

 Ancient Britons obtained the knowledge of their 

 construction from the Egyptians and Phoenicians. 

 There were, a few years ago, over twenty cromlechs 

 in the island of Anglesea alone ; but the only tradi- 

 tion I ever heard of giant or giantess in that locality 

 was a legend current amongst the Welsh people 

 that the body of a woman sixteen feet long lies 

 buried across a path leading to the church door in 

 the village of Llanedwen. That these cromlechs 

 were ever altars for druidical sacrifices seems to 

 those who have seen them utterly impossible ; and 

 as to their having been places of worship, the idea 

 is still more untenable — the space beneath many of 

 them being so small that a moderate-sized man could 

 scarcely have crept into them. Then they are mostly 

 erected on carnedds, or heaps of loose stones — a 

 most uncomfortable place for the performance of 

 devotional exercises.— Helen. E. Watney. 



Polarizing Prisms. — I believe it is generally 

 understood by microscopists that, having placed 

 the polarizing prisms in the microscope with a 

 selanite slide, all the possible changes of tint are 

 procurable by merely revolving the lower prism. 

 This, however, is not a fact, a varied adjustment of 

 the upper prism being absolutely essential in order 

 to produce certain colours. For instance, I have a 

 disc of selanite which in one position of the prisms 

 gives a blue and a yellow, while in another position 

 of the upper prism a green and a pink are produced 

 when the lower prism is revolved. Of course there 

 are intermediate shades in both cases, but in the 

 first instance no green or pink can be possibly ob- 

 tained by the revolution of the lower prism, nor in 

 the second case can yellow and blue be produced. 

 For want of a knowledge of this fact, I have known 

 friends set lightly by slides of great beauty and 

 interest. I wish I was able to assign a cause for 

 this; as yet I have been unsuccessful, but hope 

 some of your scientific correspondents will supply 

 this information, and give specific directions for the 

 relative positions of the prisms in such cases, so as 

 to produce the maximum effect, which sometimes is 

 found with difficulty. — A. N. 



Storm Glass.— In your January number I 

 observe a query on this subject which was not 

 answered. There are several receipts in print. Take 

 a long Eau de Cologne or similar bottle ; half fill it 

 with spirits of wine; take two drachms of powdered 

 camphor, half a drachm of purified nitre, and half a 

 drachm of muriate of ammonia; rub them together 

 in a mortar; put them into the bottle or tube, and 

 let it stand till the camphor is dissolved, gently 



