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ones soon killed and eat the smaller ones, so that in a short time there were scarcely above one or two left in each cell; and to this inclination of devouring their own species is attributed the scarcity of spiders, when compared with the vast number of eggs they lay. Reaumeur also affirms, that the web of the spider is inferior in strength and lustre to that of the silk-worm, and produces less of the material fit for use: The thread of the spider's web can only bear a weight of two grains without breaking; and the bag sustains the weight of thirty-six grains: the thread of a silk-worm will bear two drams and a half, so that five threads of the spider are necessary to form a cord equal to that of a silkworm; and as it would be impossible to apply these so closely together as to avoid leaving any empty spaces, from which the light would not be reflected, the lustre would consequently be considerably less: this was noticed at the time the stockings were presented to the society by M. de la Hire. It was farther observed, that spiders afford less silk than silk-worms, the largest bags of the latter weighing four grains, the smaller three grains,—so that 2304 worms produce a pound of silk. The bags of a spider weigh about one grain; when cleared of the dust and filth they lose about two-thirds of that weight. The work of twelve spiders, therefore, only equals that of one silk-worn; and a pound of silk will require, at least, 27,648 spiders. But as the bags are solely the work of the females, who spin them to deposite their eggs in, there must be kept 55,296 spiders to yield one pound of silk; and this will apply to the good ones only, the spiders in gardens barely yielding a twelfth part of the silk of the domestic kinds. Two hundred and eighty of them would not produce more than one silk-worm; and 663,555 such spiders would scarcely yield a pound of silk.

It would appear, that the spider, though usually held in abhorrence, is by no means an object of disgust to some people. The following trait, in the character of one of the first philosophers of his age, may not be generally known. In speaking of the common spider (aranea domestica), Latreille observes, "J'ai vu le célèbre astronome Lalande avaler de suite quatre gros individus de cette espèce."

The ingenious and accute entomologist, Walckenaer, as a mark of affection and regard, named a spider after one of his children, to whose precocious genius he was indebted for its discovery. "Cette espèce" (the aranea Carolina), says the French author before mentioned, "très-petite, mais très-distincte et très jolie, vit dans les bois et porte le nom du fils de Walckenaer qui la lui decouvrit n'ayant encore que trois ans. Ce monument de la tendresse paternelle est bien légitime."

MR EDITOR,

I have already endeavoured, more than once, to direct the attention of your readers to the subject of Hygrometry, a branch of science naturally interesting, and which has of late become still more so, from the ingenious discoveries of Leslie and Anderson. To the former of these gentlemen we are indebted for the best, and indeed the only, philosophical instrument hitherto employed for ascertaining the state of the atmosphere with regard to moisture; and to the researches of the latter we we some beautiful theorems for its practical application to the science of meteorology.^[1] Simple, however, and philosophical as that instrument is, it appears to me to be still capable of improvement. In its present form it can be employed only in finding the hygrometric state of the atmosphere at the moment of observation; nor have any attempts been made, as far as I know, to construct it so as to mark the extremes of dryness and moisture, in the absence of the observer. In a former communication to your Magazine, (vol. ii. p. 435.) I remarked, that the instrument might easily be made to register the greatest dryness, but that it would be difficult, I conceived, to construct it so as to mark the greatest degree of moisture. It has since occurred to me, however, that the latter object may be as easily accomplished as the former, and both on the same principle with the self-registering thermometer commonly in use. For a description of the instrument, as originally constructed by Professor

1. ↑ The researches of Mr Anderson were published, for the first time, in the Edinburgh Encyclopædia, conducted by Dr Brewster.