%S2 PHILOSOPHICAL TRANSACTIONS. [anNO 1758. 



stimulating or constricting the vessels, on which it only acts by consent, it may, 

 in small doses, be successfully used in many cases, where it has been imagined 

 to be hurtful, particularly in consumptions of the lungs, so frequent and fatal in 

 this island ; which are commonly attended with too great a laxity of the prima? 

 viae, and of the solids in general, though they seem more immediately to proceed 

 from a laxity and weakness of the pulmonary vessels ; in which circumstances it 

 must be of the utmost consequence to restore the tone of those principal organs 

 of chylification, the primae viae ; as good chyle not only corrects the acrimony of 

 the blood, which in the advanced stages of consumptions so much prevails, but 

 likewise saves a great deal of labour, which the lungs (already too much o\)- 

 pressed) must otherwise undergo from a crude and ill-concocted chyle. Agreeably 

 to this we find, in the Essays Physical and Literar)' of Edinburgh, two well- 

 vouched histories of patients far gone in consumptions, with the usual symptoms 

 of pain in the breast, cough, gross spitting of fetid matter, difficulty of breath- 

 ing, hectic fits, and morning sweats, perfectly cured in a few weeks, by the use 

 of the Hartfell-spa near Moffat; which, contrary to what is observed in most 

 natural chalybeate waters, contains a fixed vitriol of iron. 



LXXX. On the Antiquity of Glass in Wijidows. By the Rev. John Nixon, 



M.A., F.R,S, p. 601. 



Mr. N. having formerly laid before the r.s. a few observations on some of the 

 curiosities found at Herculaneum, among other articles he just mentioned a piece 

 of a plate of white glass ; and now he inquires into the uses to which such plate* 

 might be applied in the early age, to which this fragment undoubtedly belongs. 



And first it is obvious to imagine that such plates might serve for specula, or 

 looking-glasses. And indeed that specula were anciently made, not only of 

 metals, and some stones, as the phengites, &c. but also of glass, may, he thinks, 

 be collected from Pliny, who having mentioned the city of Sidon as formerly 

 famous for glass-houses, adds immediately afterwards, siquidem etiam specula 

 excogitaverat. But then it is to be observed, that before the application of quick- 

 silver in the constructing of these glasses (which Mr. N. thinks is of no great 

 antiquity), the reflection of images by such specula must have been effected by 

 their being besmeared behind, or tinged through with some dark colour, espe- 

 cially black, which would obstruct the refraction of the rays of light. On these 

 hypotheses (supposing the tincture to be given after fusion) the lamina before us 

 may be allowed to be capable of answering the purpose here assigned. 



It may further be suggested, that plates of this kind might be intended to be 

 wrought into lenses, or convex glasses, either for burning or magnifying objects 

 placed in their focus. But this designation cannot be supported by proper 

 vouchers from antiquity. On the contrary, we are informed that the ancients 



