an egg till after the middle of May, though probably an earlycoming cuckoo may produce one fooner.

The cuckoo makes choice of the nefts of a great variety of small birds. I have known its egg entrusted to the care of the hedgefparrow; the water-wagtail, the titlark, the yellow-hammer, the green linnet, and the whinchat. Among thefe it generally felects the three former; but fhews a much greater partiality to the hedgefparrow than to any of the reft: therefore, for the purpose of avoiding confufion, this bird only, in the following account, will be confidered as the fofter-parent of the cuckoo, except in instances which are particularly specified.

The hedge-fparrow commonly takes up four or five days in laying her eggs. During this time (generally after fhe has laid one or two) the cuckoo contrives to depofit her egg among the rest, leaving the future care of it entirely to the hedge-fparrow. This intrufion often occafions fome difcompofure; for the old hedge-fparrow at intervals, whilft fhe is fitting, not unfrequently throws out fome of her own eggs, and fometimes injures them in fuch a way that they become addle; fo that it more frequently happens that only two or three hedge-fparrow's eggs are hatched with the cuckoo's than otherwise: but whether this be the cafe or not, fhe fits the same length of time as if no foreign egg had been introduced, the cuckoo's egg requiring no longer incubation than her own. However, I have never feen an inftance where the hedge-fparrow has either thrown out or injured the egg of the cuckoo.'

The fubfequent part of the paper affords a strong inftance of the partial conduct of Nature. The individual fuffers pain for the benefit of the whole; and one part of the system is fupported by the deftruction of another. The young hedgeSparrows are turned out of their maternal habitation, and left cruelly to perish. It is their fofter-brother that performs the unnatural deed. The fact is curious and almoft paradoxical. The little animal contrives to get the bird upon its back, clambers up the fide of the neft, and throws it out with a jirk. When it is two or three days old it is reftlefs and uneafy, and makes extraordinary exertions to exclude its rivals.

The egg of the cuckoo is fmall, refembling the housefparrow's, and weighs from forty to fifty grains. No more than one is depofited in the fame neft. The chirp of the young cuckoo is plaintive; nor does it ever acquire the adult note during its stay in this country. It feeds upon various infects and feeds. A ball of hair of the fize of a pea, and curiously wound up, is often found in its ftomach. In this, as well as its early ferocity, it resembles a bird of prey.

Mr. Jenner promifes to give a paper upon the migration of birds, which must be extremely acceptable.

Art. XV. Of the Temperament of those Musical Inftruments in which the Tones, Keys, or Frets, are fixed, as in the

Harpsichord,

Harpfichord, Organ, Guitar, &c. By Mr. Tiberius Cavallo, F. R. S. Theoretical writers on mufic have involved the science in an air of mystery. We are glad to find Mr. Cavallo treat the fubject with his ufual fimplicity and perfpicuity. The divifions of the diatonic fcale are well known. If the whole length of the mufical chord bé reckoned 1, the first note or C will be founded by a portion as I; the fecond or D by ; the third or E by; the fourth or F by ; the fifth or G by; the fixth or A by; the feventh or B by; and the octave or c by. To thefe fimple feven founds the musicians have fince. added five intermediate notes, which are termed flats or fharps.. Thefe are, the fecond minor, the third minor, the fourth major, and the feventh major 3. The octave can be made the key, and the other notes formed by the proportional subdivifion. The fifth alfo, being expreffed by a fmall fraction, ferves fometimes for the foundation of a fcale which is termed the occafional key. These fundamentals give rife to two feries of notes which never exactly coincide. The nearest interme-, diate notes are taken, and the correction which must be applied. is termed temperament. Seven octaves are nearly equal to twelve fifths; for (3) is nearly (). The exact value of () is

12

1,498, &c. and the whole chord, being divided by this number, will give the firft tempered fifth, and this again the fecond tempered fifth, and so on. Mr. Cavallo actually tempered a monochord in this way, and tuned a harpfichord by it, which, on whatever key it was played, was harmonious throughout.

Art. XVI. Description of a new Electrical Inftrument capable of collecting together a diffused or little condenfed Quantity of Electricity. By Mr. Tiberius Cavallo, F. R. S. Mr. Cavallo, in a former paper, has pointed out the defects of the inftruments hitherto proposed for examining small quantities of electricity. In the prefent he proposes an inftrument which feems liable to few objections. The principle is the fame with that of Volta's electrophorus. To the shorter fides of a flat tin plate, thirteen inches long and eight broad, are foldered two tin tubes, which are open at both ends. Two glafs fticks covered with fealing-wax, by means of heat are cemented into thefe, and fupport the plate in a vertical pofition. Two frames of wood are faftened to the bottom boards by means of brafs hinges, and may be placed parallel and at the distance of one fifth of an inch from the tin plate. The application of the inftrument is eafy.

Art. XVII. On the Converfion of a Mixture of dephlogifticated and phlogisticated Air into nitrous Acid, by the electric

Spark.

Spark. By Henry Cavendish, Efq. F. R. S. and A. S. The beautiful experiment in which Mr. Cavendish converted into nitrous acid a mixture of the oxygenous gas and atmospheric air, by paffing through it repeated electric fparks, is delicate and laborious. Several philofophers upon the continent have triedto repeat it, but without fuccefs. Mr. Cavendish therefore dis rected the experiment to be performed before fome of the prin cipal members of the Royal Society, and thus completely ascertained his important difcovery. Atmospheric air and oxygenous gas from turbith mineral, were confined in a bent glafs tube by columns of foap-lees and quickfilver. As the acid was gradually formed, it was abforbed by the foap-lees, and produced nitre. The oxygenous gas feems to be rather more than double of the azotic in the compofition of nitre.

Art. XVIII. Experiments on the Effect of various Substances in lowering the Point of Congelation in Water. By Charles Blagden, M. D. Sec. R. S. and F. A. S. Dr. Blagden has profecuted this fubject with minute accuracy. He has made feveral curious remarks with regard to the appearance of the crystals formed, the tranfparency of the folutions, &c. which we cannot abridge. It appears that, if we denote the proportional quantities of certain falts diffolved in water by n, the point of congelation of the folutions will be expreffed by these fimple formula: Common falt 32°-n×112°, nitre 32°—48°×n, fal ammoniac 32°-120°xn, Rochelle falt 32°-22°Xn, fal catharticus amarus 32°16°Xn, green vitriol 32-10°Xn, white vitriol 32°-10°Xn. These experiments feem to confirm the principle of De Luc, that the greatest cold produced by a mixture of any falt and fnow is the fame with which a faturated would freeze. After water has taken up as much of one falt as it can diffolve, it is ftill capable of diffolving a portion of a fe cond, or even of a third falt. Dr. Blagden has found that the compound effect of thefe, in finking the freezing point, is nearly equal to the fum of the depreffions which they could make if they were separately applied. Thus a folution of of Rochelle falt, common falt, and fal ammoniac, congealed at 13°. The feparate effects are, of the Rochelle falt 32°=2°,2, common falt 112°11o,2, fal ammoniac 27. The fum of thefe depreffions is 20°,4, or at the point 11°,6, which nearly agrees. Hence the important fact, that fnow produces a more intenfe cold with a mixture of feveral falts than with a single falt. Hence alfo the frigorific powers of compound folutions. This has been noticed in the Memoirs of the French Academy of Sciences fo far back as 1700; but it has lately been revived and extended. Z

ENG. REV. VOL. XV. MAY 1790.

Dr.

Dr. Blagden next relates the refult of his experiments upor certain substances which, by equal additions, depress the freezing point of water in an increafing ratio. Vitriolic acid, whose fpecific gravity was 1,837 at 62°, congealed at 32°-98°Xn nearly; fmoking nitrous acid, whofe fpecific gravity was 1,454, at 32°-106°Xn, nearly; muriatic acid of 1,163, at 32°—80°×n, nearly; falt of tartar 32°-54°Xn, nearly; mineral alkali, 32°-21°n; volatile alkali 32°-68°×n; spirit of wine, of the fpecific gravity 829, at 32°-70° xn. Water begins to expand at the temperature of 40°; and it appears that an addition of falt reduces the expansion to 8° above the depreffed point of congelation.

Art. XIX. Additional Experiments and Obfervations relating to the Principle of Acidity, the Decompofition of Water and Phlogifton. By Jofeph Priestley, LL.D. F. R.S. With Letters to him on the Subject, by Dr. Withering and James Keir, Efq. This paper contains fome additional remarks upon the experiment which this ingenious philofopher made by inflaming a mixture of the oxygenous and hydrogenous gafes. The quantity of acid produced was fo fmail that the doctor was at a lofs to decide its fpecies. His philofophical friends examined the liquor by various tefts, and found it to be nitrous acid. have already fhewn, we hope, that this minute portion of acid is derived from the impurity of the gafes, and that the experiment does not affect the theory of Lavoifier. Phlogifton is the proteus of the conflitutional chemifts. It is a phantom which affumes various fhapes, according to the fancy of the inquirer. Many phenomena, indeed, can be well explained by both fyftems. In the one there is an abstraction; in the other an accumulation. But the theory which is formed upon the continent poffeffes a clearness, a precifion, and an elegance, which set it upon a firm basis.

Art. XX. On the Probabilities of Survivorships between two Persons of any given Age, and the Method of determining the Values of Reverfions depending on thofe Survivorships. By Mr. William Morgan. Communicated by the Rev. Richard Price, D. D. F. R. S. The hypothesis of De Moivre with regard to the probability of the duration of human life is extremely fimple, and tolerably accurate. He fuppofes that out of eightyfix perfons born at the fame time, one dies annually till the whole number be extinguished. The chance that a person, 86-n therefore, fhall attain the age of n years is that of n+1, 86

85-n 86

that of n+2,

84-n
86

&c. Whence the chance that a perfon

85-7
8672

person of the age n shall survive the present year is 35; and the

chance that he shall die within the year is

86

By the help

of these data the feveral problems in the doctrine of annuities can be folved with confiderable elegance. But the hypothefis is particularly erroneous with regard to the early and the very advanced periods of life; and in the cafe of joint-lives and of furvivorships, the errors are prodigioufly increased. Recourse muft therefore be had to tables of real obfervations. Mr. Morgan, in the paper before us, has pointed out fome mistakes into which his predeceffors have fallen, and has fhewn the proper mode of inveftigation-Suppofe that the ages of two perfons, A and B, were given to determine the probability of furvivorship. Let A denote the number of perfons living at the age of A the younger, and a', a", a", &c. the decrements of life at the end of the Ift, 2d, 3d, &c. years. Let b represent the number of persons alive at the age of B, and c, d, e, &c. thofe living at the end of the ift, 2d, 3d, &c. years. The event that B fhall furvive A during the first year may take place in two ways; either A may expire during that time, or both. The chance that A dies the first year is, and that B survives that time is

therefore, that both events take place is ac

ab

b

the chancė,

The probability

that both lives are extinguished during the first year is a

a

b= this fraction, or a'(bc), will therefore exprefs the chance that

but the priority of the deaths is indifferent; the half of

zab

A dies firft. Hence the whole probability that B will furvive a' (b-c) a'(b+c); and fo on for

a'c in the first year is + ab

the fucceffive years.

viving A will be =

zab

or

zab

Hence the whole probability of B's furI 1b+c

Mr. Morgan has taken the trouble to calculate, from thefe principles and the Northampton Obfervations, fome useful tables, which accompany this paper.

Art. XXI. An Account of a remarkable Tranfpofition of the Vifcera. By Matthew Baillie, M. D. In a Letter to John

Z 2

Hunter,