- -. 



SLEEP. 



SLEEP. 





be indicated by all the phenomena a the grand agent in the produc- 

 tion of slaty clearage. Only one tolerably successful effort ha* been 

 made experimentally to reproduce thi* structure by art Mr. U. W. Fox 

 ha* caused electrical current* to traverse a mats of moist clay, and ha* 

 obeerred in consequence the formation of numerous fisuro, more or 

 less similar to slaty cleavage, in planes parallel to the vertical bounding 

 surface* of the mass, and at right angle* to the electrical currents. 

 The exact application of this experiment U not understood. Perhaps 

 however, conjoined with the admUsion that the great movements of 

 strata, by which apparently slaty cleavage was determined, depended 

 on disturbed equilibrium of internal heat, which might, or rather 

 must, have developed electrical currents, this solitary experiment may 

 be the commencement of a right mode of more extensive iuquiry 

 embracing the many circumstances of chemical nature, stratified 

 arrangement, disturbed position, and proximity of igneous rocks, which 

 must all b included in a good theory of slaty cleavage. 



For economical purpose* there appears little chance of obtaining in 

 the British Island* good Slate (properly *o called) from any but the 

 ancient argillaceous strata superposed on mica-schist and gneiss, and 

 covered by old red-sandstone or mountain limestone. From these 

 strata in Scotland, Cumberland, Westmoreland, Yorkshire, Charnwood 

 Forest, North Walei abundantly, South Wales, Devonshire, Cornwall, 

 the north and south of Ireland, Mates of various value are dug. The 

 thin flagstone of the coal formation iu many parts of England and 

 Wales the laminated sandy limestone of Stonesfield, Colly wiston, &c., 

 which are often called slates, and are extensively used iu roofing, are 

 all obtained by natural partings parallel to the stratification. True 

 slate is split by wedge* from the apparently solid rock along planes 

 often no more discoverable than those of a real crystal. In colour it 

 is purple, blue, green, yellowish, or almost white, or striped across 

 the planes. In some slates (west of Scotland, Ingleton, &c.) crystals 

 of cubical iron pyrites are scattered. Much of the Cumberland slate 

 appear* full of fragments (Borrowdale), and some contains chiastolite 

 (Skiddaw). 



In the United States, a good material is obtained in Maine at 

 Barnard, Piscataquiea, Kennebec, Biugham, and elsewhere; also in 

 Massachusetts, in Worcester county, in Boylston, Lancaster, Harvard, 

 Shirley, and Peperell; in Vermont, at Gailford, Brattleborougu, 

 Fairbaven, and Dummerston ; in Hoosic, New York ; on Bush Creek 

 and near Unionville, Maryland ; at the Cove of Wachitta, Arkansas. 

 At Rutland, Vermont, is a manufactory of slate pencils, from a 

 greenish slate. 



Thine slate rocks are also used for gravestones in New England 

 cemeteries. It U however liable to fall to pieces. 



Drawing State is a finer and more compact variety, of bluish and 

 purplish shade* of colour. The best slate* come from Spain, Italy, 

 and France. A good quality is quarried in Maine and Vermont, United 

 States. 



NorattUHf, /font-Mate, or Whct-Ktone, is a fine grained slate, con- 

 taining considerable quartz, though the grains of thin mineral arc not 

 perceptible. It occurs of light and dark shades of colour, and compact 

 texture. 



Aryillite is a general term given to argillaceous or clay-slate rocks. 

 Many shales or argillites crumble easily, and are unfit for any purpose 

 in the artc, except to furnish a clayey soil. 



A /urn Miale is any slaty rock which contains decomposing pyrites, 

 and thus will afford alum or sulphate of alumina on lixiviation. 



Bituminoiu Shalt is a dark coloured slaty rock containing some 

 bitumen, and giving off a bituminous odour. 



Plttmbaginout Schitt is a clay slate containing plumbago or graphite, 

 and leaving trace* like black lead. 



The Pipatont of the North American Indians was in part a red 

 claystone or compacted clay from the Coteau de Prairies. It has been 

 named Catlinile. A similar material, now accumulating, occurs on the 

 north shore of Lake Superior, at Nepigon Bay. Another variety of 

 pipestono is a dark grayish compact argUlite ; it is used by the Indians 

 of the north-west coast of America. (Dana.) [AUA.LMATOI.[TE ; MICA- 



SCHMT.l 



SLEEP, the periodical repo-e of the organs of the senses, and of 

 the greater number of the intellectual faculties and voluntary move- 

 ment*. The above indeed is by no means a satisfactory definition ; 

 bat it i*, * with life, far easier to describe it* phenomena than to 

 define it* nature. 



True sleep i* peculiar to tho Mammalia and to Bird*. Tho lower 

 animal/i indeed rest from time to time, ami withdraw themselves from 

 the external world, but having no external eyelids, they cannot exclude 

 all influence from without. Fish conceal themselves behind a stone 

 or near the bank of a river; crocodiles hide themselves in the mud ; 

 and tortoise* creep into holes. The higher animals likewise usually 

 eek oat some place of retirement to sleep in, and dispose themselves 

 in a posture which either is maintained with little muscular effort, or 

 is favourable to the preservation of warmth. 



The approach of sleep i* announced by diminished activity of 

 mind and lo-s of the power of attention. The senses become blunted 

 to external impressions, and we feel an unconquerable desire for 

 stillueo* and repose. Our ides* grow more confii'od our sensations 

 more obscure our sight fails us and if our ears still perceive sounds 

 they are indistinct, and seem a* though distant Tho eyelid* close, 



the joint* relax, we instinctively assume an easy position, and fall into 

 a sleep, which at first is deep, then soft and gentle, and becomes 

 gradually less sound a* the time for waking approaches. 



Physiologist* are accustomed to distinguish what are termed the 

 organic or vegetative from the animal properties of living bring'. 1'y 

 the former are understood development, growth, excitability, &c., 

 those power* in abort which are common to plant* and animals ; by 

 tho latter, thorn properties which are peculiar to animal*, such a* 

 sensation and voluntary motion. During sleep the organs of vegetative 

 life continue to discharge their functions with scarcely less activity 

 t'l.m in the waking stat-.-. Their repose is independent of sleep, and 

 occurs at very different times. The heart rests between each pul- 

 sation, the muscle* of expiration and inspiration are in a stato of 

 alternate action and repose, and the peristaltic motions of the intestine* 

 have their distinct periods of remission. The pulse and respiration 

 however become slower during sleep, and digestion seems to go on then 

 less perfectly than in the waking state. The temperature of the body 

 sinks during sleep, owing to the diminished nervous energy, and to 

 the same cause may be ascribed the increased susceptibility of persona 

 to rheumatism and other effects of cold when asleep. 



Not only are the functions of organic life little affected by sleep, 

 but even those of animal life are not in a state of complete repose. 

 It would not be possible to make a dead body remain in those postures 

 which we assume when asleep, and our eyelids are not closed except by 

 muscular action. Some animals sleep standing, a* the horse ; bird* 

 do so also, sometimes standing on one leg. When very weary, wo 

 sleep even in the most constrained positions; soldiers have been 

 known to sleep while marching, postilions on horseback, and fiddlers 

 at a fair have continued to play even when through weariness they 

 have fallen asleep. The numerous instances of sonnambulism on 

 record show how high a degree of activity of the animal functions is 

 compatible with sleep. 



Animals in general require less sleep than man : thus, for instance, 

 four hours are sufficient for the horse. Those animals whose blood 

 circulates very rapidly, whose motions are peculiarly energetic, an. I 

 their senses very acute, usually sleep more lightly, and for a shorter 

 time than others. The timid herbivorous animals sleep less, .v 

 profoundly than the bolder Oarnivoni. In man the want of sleep 

 varies at different ages; the new-born infant sleeps almost continually, 

 whilo persons in middle life can do with less sleep than children or 

 very old persons, and women require less sleep than men. From six 

 to eight hours a-day are usually passed in sleep, but habit exercises a 

 great influence in determining the amount of repose required. John 

 Hunter and Frederick the Great did not sleep more than four hours 

 doily, while some sluggish persons spend nearly half their time in 

 sleep. In extreme old age much sleep sometimes become* necessary. 

 De Moivre, when eighty-three years old, was awake only during four 

 hours out of the twenty-four ; and Thomas Parr, towards the close of 

 his life, was almost constantly asleep. Children sleep very soundly, 

 old persons are easily disturbed, men sleep more profoundly than 

 women, and sleep is always sounder after considerable weariness 



There are some conditions which favour the occurrence of 

 Stout and full-blooded persons, and those of au excitable but easily 

 exhausted frame, require mora sleep than such as are thin, or who, 

 though equally excitable, are more energetic, and less easily tird. 

 Abuudaut food induces sleepiness, and also wine and other stimulants. 

 A class of medicines arc known by tho name of narcotics, 

 peculiar action is to induce sleep. Ease and quiet of mind con iuo- 

 to it, but the weariness of hopeless grief is likewise followed by sleep. 

 Certain external causes favour sleep, such as the warm bath or friction 

 of the surface of the body. Extreme cold is a powerful and most 

 dangerous narcotic ; it induces a sleep from which there is no waking. 

 Such a sleep it was which nearly proved fatal to Dr. Solander, 

 with Sir .1. Banks in Tierra del Fuego. 



We have not yet noticed one very important character of sleep its 

 p -nodical return once in ev. ry twenty-four hours. Tho idle person 

 sleeps as well as tho diligent who has passed his tiinn iu exerting hi* 

 powers of mind or body. Sleep usually occurs at night-time, and wo 

 arc awake during the day ; but the day may become tho time for 

 sleep, and night for watching, if a person's occupation so require. 

 Many animals sleep during the day, and watch or pursue their prey at 

 night. We cannot then regard tho periodical return of sleep a* 

 dependent on the simple alternation of day and night, or merely as 

 the result of bodily fatigue, since it is known that extreme weariness 

 will prevent sleep. The alternation of sleep and waking is essentially 

 connected with something iu tho nature of animals, to which their 

 are many analogies. Tho succession of the seasons and of day and 

 night, the ebb and flow of the sea, tho daily variations in the electricity 

 of the air, in the rise and fall of the barometer, and the rrular declina- 

 tion of the magnetic needle eastward and westward, at different hours, 

 illustrate the same law of periodical action which is displayed iu the 

 unvarying alternation of sleep and waking. " We may," says M 

 "regard sleep and the waking state as the result of a species of 

 antagonism between tho organic anil the animal life, in which the 

 functions, governed by the mind, become free to act, while at 

 other time* they are repressed by the organic force acting in obi i 

 to a liwof creative nature. In sleep, when the animal fun- 

 entirely or for tho most part cease, the organic processes are almost 



