By the help of this Problem a Man may talk to his Friend at a very considerable distance, so that those in the middle space shall hear nothing of what passed betwixt them.
FIG. V. TAB. III.
Semiplanum Sphæræ Phonicæ seu Acousticæ.
You are to conceive that (rude) Semiplane, as parallel to the Horizon: For if it be perpendicular thereunto, I suppose the upper extremity will be no longer Circular, but Hyperbolical, and the lower part of it suited to a greater Circle of the Earth. So that the whole Phonical Sphere (if I may so call it) will be a solid Hyperbola, standing upon a Concave Spherical Base. I speak this concerning Sounds made (as usually they are) nigh the Earth, and whose Sonorous Medium has a free passage every way. For if they are generated high in the Air, or directed one way, the case will be different; which is partly design'd in the inequality of that Draught.
A Discourse concerning the Modern Theory of Generation, by Dr. George Garden of Aberdeen, being part of a Letter to Dr. William Musgrave, L. L. D. Reg. Soc. S. and by him communicated the Royal Society.
THE Subject I pitch upon, is that of the Formation of Animals. You know how wide and unsatisfying Men's Conjectures were upon this Head, until this Age, in which first the deservedly Famous Dr. Harvey discovered the proper place of the Formation of the Chick in the Cicatricula of the Egg, and the Formation of the Parts so far as was discernable by the naked Eye; and after him Malpighius, by the help of exact Glasses, observ'd the first Rudiments of it there, both before and after Incubation: And R. de Graef, and others, having upon many Observations concluded, that the Testes Fœminei were the Ovaries of Females, and consequently that all Animals were ex ovo; they began from hence to infer, that the Rudiments of each Animal were originally in the respective Females, and that the Male contributed only to give a new Ferment to the Mass of the Blood and Spirits, by which means a spirituous Liquor (which the Blood in its ordinary Ferment could not produce) did insinuate it self into the same Ducts and Pores of the Rudiments of those Animals, which were in greatest forwardness in the Ovary, and so extend and enlarge all their Parts, and at last bring them to perfection, as Mr. Perrault does ingeniously discourse in the third Part of his Essais de Physique; till now at last Leowenhoek has discover'd an infinite number of Animalcula in semine marium of all kinds, which has made him condemn the former Opinions about the Propagation of all Animals ex Ovo.
Now upon comparing the Observations and Discoveries which have been made with one another, these three things seem to me very probable. 1. That Animals are ex Animalculo. 2. That these Animalcles are originally in semine Marium & non in Fœminis. 3. That they can never come forward, nor be formed into Animals of the respective kind, without the Ova in Fœminis.
The first of these seems probable from these three Observations. 1. That some such thing has been so often observ'd by Malpighius, in the Cicatricula of an Egg before Incubation, as the Rudiments of an Animal in the shape of a Tadpole, as may be seen in his first, and in his repeated Observations de formatione Pulli in Ovo. 2. The sudden appearance and displaying of all the Parts after Incubation, makes it probable, that they are not then actually formed out of a fluid, but that the Stamina of them have been formerly there existent, and are now expanded. The first Part of the Chick which is discovered with the naked Eye, is, you know, the Punctum saliens, and that not till three days and nights of Incubation be past; and then, on the fifth day, the Rudiments of the Head and Body do appear. This made Dr. Harvey conclude, that the Blood had a being before any other Part of the Body; and that from it, all the Organs of the Fœtus were both form'd and nourished: But by Malpighius's Observations we find that the Parts are then only so far extended, as to be made visible to the naked Eye, and that they were actually existent before, and discernable by Glasses. After an Incubation of thirty hours, are to be seen the Head, the Eyes, and the Carina with the Vertebræ, distinct, and the Heart. After forty hours its Pulse is visible, and all the other Parts more distinct, which cannot be discerned by the naked Eye before the beginning of the fifth day; from whence it seems probable, that even the so early discovery of those Parts of the Fœtus by the Microscope, is not the discerning of Parts newly formed, but only more dilated and extended by receiving of Nutriment from the Colliquamentum; so that they seem all to have been actually existent before the Incubation of the Hen. And what Swammerdam has discovered in the transformation of Insects, gives no small light to this; whilst he makes appear in the Explanation of the 13th Table of the General History of Insects, that in those large Eruca's which feed upon Cabbage, if they be taken about the time they retire to be transformed into Aurelia's, and plung'd often in warm Water to make a Rupture of the outer Skin, you will discern through the transparency of their second Membrane, all the Parts of the Butterfly, the Trunk, Wings, Feelers, &c. folded up. But that after the Eruca is chang'd into an Aurelia, none of these Parts can be discern'd, they are so drencht with moisture, tho' they be there actually form'd. Another Consideration is from the Analogy, which we may suppose between Plants and Animals. All Vegetables we do see proceed ex Plantula, the Seeds of Vegetables being nothing else but little Plants of the same kind folded up in Coats and Membranes; and from hence we may probably conjecture, that so curiously an organized Creature as an Animal, is not the sudden Product of a Fluid or Colliquamentum, but does much rather proceed from an Animalcle of the same kind, and has all its little Members folded up according to their several Joints and Plicatures, which are afterwards enlarged and distended, as we see in Plants. Now tho' this Consideration alone may seem not to bear much weight; yet being join'd to the two former, they do mutually strengthen each other. And indeed all the Laws of Motion, which are as yet discovered, can give but a very lame account of the forming of a Plant or Animal. We see how wretchedly Des Cartes came off when he began to apply them to this Subject; they are formed by Laws yet unknown to Mankind; and it seems most probable, that the Stamina of all the Plants and Animals that have been, or ever shall be in the World, have been form'd, ab Origine Mundi, by the Almighty Creator within the first of each respective kind. And he who considers the Nature of Vision, that it does not give us the true magnitude, but the proportion of things; and that what seems to our naked Eye but a Point, may truly be made up of as many Parts as seem to us to be in the whole visible World, will not think this an absurd or impossible thing.
But the second thing which later Discoveries have made probable, is, that these Animalcles are originally in Semine Marium & non in Fœminis. And this I collect from these Considerations: 1. That there are innumerable Animalcula discover'd in Semine Masculo omnium Animalium. Mr. Leewenhoeck has made this so evident by so many Observations, that I do not in the least question the truth of the thing. The reason of their Multitude, and some of the Difficulties which arise thereupon, he has cleared to very good Purpose, so that I shall not repeat them. 2. The observing the Rudiments of the Fœtus in Eggs, which have been fecundated by the Male, and the seeing no such thing in those which are not fecundated, as appears from Malpighius his Observations, make it very probable that these Rudiments proceed originally from the Male, and not from the Female. 3. The resemblance between the Rudiments of the Fœtus in Ovo, both before and after Incubation, and the Animalcle, makes it very probable, that they are one and the same. The same Shape and Figure which Mr. Leewenhoeck gives us of the Animalcle, Malpighius likewise gives of the Rudiments of the Fœtus, both before and after Incubation; yea, and even the Fœtus's of Animals do appear so at first to the naked Eye, so that Dr. Harvey does acknowledge that all Animals, even the most perfect, are begotten of a Worm, De Gen. Anim. Ex. 18. 4. This gives a rational account of many Fœtus's at one Birth, especially that of the Countess of Holland, and how at least a whole Cluster of Eggs in a Hen are fecundated by one Coition of the Male. 5. This gives a new light, as it were, to the first Prophecy concerning the Messiah, that the Seed of the Woman shall bruise the Head of the Serpent, all the rest of Mankind being thus most properly and truly the Seed of the Man. 6. The Analogy I have already mentioned, which we may rationally suppose between the manner of the propagation of Plants and Animals, does likewise make this probable. Every Herb and Tree bears its Seed after its kind; which Seed is nothing else but a little Plant of the same kind, which being thrown into the Earth, as into its Uterus, spreads forth its Roots, and receives its Nourishment, but has its form within its self, and we may rationally conjecture some such Analogy in the Propagation of Animals.