Pyre no mycetes (pire" nomisetez)

pl. [NL., the sparrows, now usually placed in the genus Pa er: so called because the common house sparrow often builds its nest in towers. pyrgoidal (per-goi'dal), a. [ of the form (m-2) r3 - (2m-7) r2+ (2m- 7) r. pyrheliometer (per-he-li-om'e-tèr), n. [ instrument devised by M. Pouillet for mea suring the intensity of the heat of the sun. It consists of a shallow cylindria cal ve el of thin silver or copper, containing water or mercury in which a thermometer is plunged. The upper surface of the ve el is covered with lampblack, so as to make it absorb as much heat as po ible, and the ve el is attached to a support in such a way that the upper surface can always be made to receive the rays of the sun perpendicularly. The actual amount of heat absorbed by the instrument is calculated by ordinary calorimetrical means: the area of the exposed blackened surface is known, and the amount of water or mercury which has been raised through a certain number of thermomet IMG:content-1377.png:[merged small][ocr errors][merged small][merged small][merged small] a, blackened disk exposed to sun's rays, the direction of which is indicated by dotted lines, as db, c, column of delicate ther mometer whose bulb is inserted in of the support. box beneath a, e, place IMG:content-1378.png:[blocks in formation]