must be accelerated as the earth approaches its Perihelion. This, if it be true, affects practical Aftronomy in every part, as thereby a new Equation to find Equal Time becomes neceffary, and is a material point in afcertaining the Longitude. The truth of this new affertion may be difcovered by fixing a telescope in the Meridian, fo as to obferve daily the tranfit of a fixed ftar, by a good clock. But, as the motion of a pendulum is altered by heat and cold, the clock ought to be placed in fome deep pit, where the heat remains always nearly the fame. The pofition of the moon alfo is to be carefully regarded, in making the obfervations: for the motion of a pendulum clock is likewife changed by the difference of Gravitation to the earth, from the different pofitions of the moon, as appears by the theory of the tides. For this reafon the observations would become more certainly decifive, if two or three telescopes be fixed fo as to obferve the tranfits of as many ftars, which pass at fome hours distance from each other, and the nearer they are to the Zenith the better.

In order fully to comprehend the force of the preceding arguments, it is to be observed, that we have no idea or conception of the primitive powers, or of their manner of acting; we have only ideas of the effects produced by them. We have no idea of the refifting power in matter, or of its manner of acting, other than the effect of it, in refifting any other power which makes it change its prefent ftate. We have no idea of the moving power, or of motion, other than change of place, which evidently is not the action, but the effect of the action.

We have therefore no other method of difcovering the rules or laws of action, in the primitive powers, but by drawing general conclufions from a diligent obfervation of numerous effects of thefe powers, which are commonly called phenomena. If then, from the general deductions or laws of action laid down in the Principles of Action, the phenomena of the Planets, the cohesion of the parts of bodies, the elasticity of the air, the refraction and reflection of Light, and phenomena of colours, and the furprizing phenomena of Electricity (by the Author's fon) be more clearly explained, than has been done by any other method, it must greatly confirm the truth of thefe principles, and all these phenomena are attempted to be explained, in the copy for a new edition of the Principles of Action.

From a diligent obfervation of numerous phenomena, the Author deduces this general law of the Action of Light.

That

That Light, if nothing hinders, gives motion to bodies, in the direction of its rays; but if it cannot in this direction, it gives motion in any other direction the nearest to it, where it meets with least resistance.”

A Treatise on the three different Digeftions, and Difcharges of the Human Body; and the Difeafes of their principal Organs. By Edward Barry, M. D. F. R. S. Profeffor of Phyfic in the University of Dublin, and Physician-General to his Majefty's Army in Ireland. 8vo. 6s. Millar.

TH

HIS excellent medical performance bears all the marks of the Author's ability and experience in his profeffion. It was the refult, as the preface informs us, of his frequent reflection on the Diseases of the Lungs, and the Nature of Nutrition; on which he had publifhed a treatise above thirty years paft, which his present maturer judgment modeftly represents to him as an imperfect and too early performance. We find then his further confideration of Pulmonary Confumptions has led him into a profound and retrospective investigation of that defective state of all thofe Digestions and Discharges of the body, which may, more or lefs, difpofe to that, and to fuch other chronical difeafes, as are the particular fubjects of the present treatise.

As it would be extremely difficult to make a ufeful abstract of a work, into which the Author has crowded, as we may fay, great medical knowlege and literature, in a manner more close and appofite, than oftentatious; and as the entire treatise [which, he juftly obferves, it was more difficult to contract into the limits he had prescribed it, than it would have been to have enlarged it] deferves the ftrict confideration of every young Regular and may usefully entertain even thofe more advanced, especially on the Diseases of the Langs; we shall therefore chiefly attempt to give a general view of the order and connection of fome of his chapters, with their different sections; inserting a few of many fuch paffages as appear to us new, and more properly Dr. Barry's own fentiments and fuggeftions, which will at the fame time exhibit his manner of reasoning, and of writing.

The first chapter treats of the First Digeftion; as it was neceffary to give fome notion of its compleat and falutary ftate, in order to a better conception of its morbid or defective one. This falutary state of Digeftion is very clearly dif

Ee 2

played

played here, to any who have attentively furveyed the ftoinach, and its fituation amidst the contiguous and adjacent Vifcera. But as this Gentleman, with all his liberal regard to reputable medical Writers, is actuated by a greater deference to Fact and Reason than to Authorities; after obferving the calculations of Pitcairn, (on Borelli's Principles) of the force of the ftomach, which he juftly calls wild computations; and making a practical diftinction between the abfolute force which a Muscle can exert, and that real force which it ufually does, he rationally adds, page 18, fpeaking of the ftomach: For its powers are much weaker than they are generally fuppofed to be, and not capable of diffolving the folid parts of animal or vegetable bodies; but only of attenuating, and expreffing the fluid parts. This is confirmed by repeated and obvious experiments; for Currants, Grapes, or any other Fruit, or Seed, fwallowed whole, and < entire, remain fo in the excrement.

'Hence the reafon plainly appears, why the ftomach is not diffolved by its own action; of which it must certainly have been in great danger, if it contained an active ferment, or could excite fuch a powerful attrition, as might be capable of diffolving, or grinding the folid parts of such food, as are • often received into it, and which have as ftrong a cohesion ་ as the ftomach itself.'

In mentioning the Peristaltic Motion of the Inteftines, as a confiderable inftrument in a further elaboration of the first Digeftion, he thus ingeniously fuggefts the analogy between this motion and that of the Heart; and the true, or most probable, Reafon we have met with, why the Lacteals have never as yet been injected.

Is not this muscular action alternately relaxed, and contracted, fomewhat analogous to that of the Heart? and is not the power of Abforption alone, infufficient to receive and propel the Chyle through the Lacteals, whofe motion acquires no immediate influence from that of the Heart? On which account, this defect is not only fupplied in their origin, but through their whole course, by a various and exquifite mufcular motion.

Hence appears the reafon, why the Lacteals could never by any art be injected in dead bodies? Their oblique fituation, and minutenefs, requiring this peculiar motion, to overcome their refiftance.-Van Helmont, therefore, might with more juftice, have placed his Archaeus there, than in

• the

the Pylorus, which he confidered as a careful Centinel, ⚫ that denied a passage to any thing injurious to life.'

Having represented the extraordinary proportion of Nerves fent to the Stomach and Intestines, which are more large and numerous than feem neceflary for their mufcular motion; and after noting, especially, their uncommon proportion and diftribution throughout the Mefentery, he makes the following curious suggestion.

It is therefore more than probable, that the Chyle in its paffage through the Mefentery, is impregnated with a great quantity of Animal Spirits.'

Finally, under this article of the firft Digeftion, Dr. Barry fuggefts, the reason, why perfons of the ftrongest conftitution are most apt to be coftive; fuppofing, in fuch, the finer part of the Faces to be admitted into the abforbent Veins of the great Inteftines, which, he imagines, like fo many volatile Spirits, raised by distillation from putrefcent animal bodies, greatly to contribute to animate the whole machine.'--This abforption of part of the Faces into the blood feems, at first fight, to give us fome notion of the mafs becoming more. impure and feculent from it; upon which opinion we find clyfters often directed in the beginning of acute diseases, to cleanfe and empty the inteftinal canal: and, indeed, our Author himself fuppofes, page 105, the retention of the • Excretions, all of which,' he obferves, are of the putrefcent kind, to be a powerful and frequent caufe of pu⚫trefaction in animal fluids.' And here by the way we may query, whether the difagreeable odour of the Perfpiration in fome vigorous perfons, especially after much labour or exercife; and even the Fætor of the breath in others, (whofe Lungs are found) may not, in part, refult from a vaporous discharge of fuch feculent particles from the circulation, into which they were abforbed in a groffer confiftence? Be this however as it may, the admiffion of it will not invalidate our Author's inference on this point; as thofe feculent particles may be innoxious, and even ufeful, in a healthy state, which would aggravate a difeafe, and particularly a putrid one. For as the ftimulation from the contents of the blood, in its natural crafis, has been confidered by excellent Physiologists, as one cause of its circulation through the Heart; an unusual defect of its ftimulating principles would very probably conduce to its feebler motion, and the diforders refulting from fuch defect. On a cause very fimilar to this Dr. Barry establishes the reafon, p. 33, 34, why perfons of a low nervous conftitution, are generally fo much depreffed by the lightest Purgatives:

Ee 3

and

and why that depreffion is, in a great measure, prevented, or removed, by the ufe of Afa Foetida and volatile Medicines. These facts occurring, not rarely, in practice, reflect no inconfiderable light on this hypothefis, which, however doubtful to fome, may prove the leaft indigeftible to those who fhall reflect the most upon it.-The only fection annexed to this chapter, of the First Digeftion, treats of a Depraved Appetite and Indigeftion; and contains many judicious remarks, inferences, and directions, recommending a few such medicines as feem indicated from a very rational confideration of its different causes.

The second chapter is appropriated to the Second Digeftion, or the Commutation of the Chyle into fuch a fine Serum, as is qualified to pervade the finest veffels of the body. Our Author confiders the Lungs as the principal organ of this operation, and very practically remarks here, That as all the new Chyle muft pafs the Lungs, before it is tranfmitted into the general arterial fyftem, Medicines will arrive to the Lungs with their virtues and qualities more analtered, than to any other more diftant bowels, to which they must be diftributed through the arterial fyftem, in much lefs quantities, and more changed.' The only fection annexed to this chapter, treats of the Tenacity of the Blood; in which the Author judiciously distinguishes that Tenacity, which it receives through too intenfe a motion and heat, from that vifcid texture arifing from too languid a circulation, whence the globules are more light and diffolved, and their cohesion weaker. He obferves the great error in practice, of attempting to remove the first by ftimulating volatile medicines and blifters, which, he thinks, must increase its tenacity, by increafing its heat and motion; and directs a rational procedure in this tenacity, as well as in this vifcidity, of the blood.

The third chapter treats of Urine, and the Diseases of this fecond Discharge. He confiders this fluid as the fuperfluous or excrementitious parts of the Chyle, after its elaboration into Serum; and in the immediately fubfequent fections, of the Nature and Formation of Calculous Concretions, he opposes the opinion of their being formed from tartareous or acid alts; truly affirming, that they are of a contrary nature, confifting of terreftrial, oily, and alkaline parts, [which has appeared from experiments] and adding, that their hardness will always be proportioned to the denfity of the oily, and he minutenefs of the terreftrial parts. The force of Lithontriptic Medicines, he obferves, muft confift in attenuating

and