Frankfort, July 10, 1873. Friejíd Pond : Whileupon the subject of collatoral aids to the 8tudy of Natural History we caunot well omit to mention the very interesting Aquarium at Berlín, of wuich Dr. Brehoi is Director. In America we thitik of an Aquarium as a sort of ornamental reservoir of a few cubit feet, in which a few ferns or water planta and three or tour varieties of water animáis are managing to protract tbeir existence. It was no such pluything as this we had the pleasure of visiting at Berlin. TJpon entering the building we did not at once perceive the objects we had anticipated ; but upon either hand, in theirglaascages, were great boas, lizards, and other reptiles, of varieties which happily are quite rare in températe latitudes. Birdsalsoof beautifulplumage and uierry voice? or singular habits were quite at home in their rustic and spacious abode and wêre busy in all the natural oocupations of their native homes : nest building, incubation, &c. Amoiig these the work of the weaver bird wasparticularly curious. Instead of ascending as in ordinary museums we uow descended, and along our " winding way " to a depth corresponding with two or three stories and through a wide lateral extent we found ourselves in constant delight aud surprise at the great variety and amazing success o' the tieatment here adopted, not merely in thesusteuan:e but in the propagation of such a large number of marine animáis. The arrangement is made doubly attractive by being subterrean, the tanks being, as it were, be hind glass windovvs and lighted trom above outside the rooky grotto or cave ehambers about whicb. we walked. Tbis made every object within the various receptacles distinctly visible, and the puri'y oi the sea waier as well as its peculiar fitness tor the purpose was . insured by au unceasing iufusion into each divisiou of the aquarium of water daily bronght fresh l'roui the sca at Hamburg. The uuppy resulta of all this careful arrangement were appaient, aud here we had the pleasure of seeing not merely a great variety of físhes of singular habits aud appearance, but shell fisu of many kinds, as well, were thriving as if in their native element. But more curious and gratifying was it to watch the various forms of still lower organisms : the star fish, sea egg, coral uiseots, sponges, sea anemones, polypi, and many uameless specimens of these lowest forms of mariue hfe, with scarcely auything in comuiuu with the ordinary specimens of life, and inanifesting the presence of something more than mere vegetable vitaiity ouly by sohio gentle or spasmodic exhibition of contráctil or expansive power, in the transparent worm like bracchia, or in the creation of currents in their immediate vicinity indicative of some fonn of respiratiou or demand for nutriment. Som of these objects weie extremely beautif'ul iu their forms and various colors, and it has never been our fortuno to have seen anything more f uil of profound interest. We could thus witness the habits and hauuts of these singular beings quite at our ease and in a much greater variety than we would be likely to find were it even practicable to wander ai will far down upon those ocean sands "Where thepurple mullet and the gold fiahrove." There must have been as many as 50 or GO of these windows of solid glass, five or six feet long by thrue or four feet high, through which we could view these novel sights, and iu uo single instance did we notice anything to indícate that the many varieties of life lacked anything to make them as vigorous and perfect as if quite at liberty in their ocean hannts. Of course we did not fail to make the travelers pilgriniage to Potsdam where, more than at Berlin, evurything breaths of reraniscences of the Great Frederick, who there erected the fatnous Sans Souci palace, A. D., 1715, and made it his almost constant homo. Here, also, after the close of the seven year's war he eonstructed his new palace, as it is called, upon a scale of grandeur and costliness muoh greater than the former. Other palaces are also located Viere,- in one of which tbe late king re&ided and in another, B,ibelsburg, the preesut Euiperor is spending the summer. It is a pleasant city of over 40,000 inhabitants, and judgirig from the uumber of cariages wuiting at the depot they are reaily to escort au equal nuuiber of strangers to all the palaces, - for acousideration named by themselves. Escaping from the city liiuits we wend onr way to the obelisk which is near the entrance to tho Park at its eastern extremity, and from this point directly to the front of the New Palace a perfectly straight avenue leads through the forest of splendid trees over a rnile in length and as Ie vel as if giaded for a floor. Persons seen at one end of this vista appeared like very pigmies to those at the other. Abnut one-fourth the way frorn the obelisk the avenue expands into a circular space, with a fine inarble basin and fountain figures in the center, and about its circumference are various groups of statuary. Crossing the wide open space in front of the palace, laid out as a flovver garden in ornamental designs, but at the time of our arrival so scorchingly hot that we did uot tarry to examine it, we soon got admission with others iiito the palace. The first room was something decidedly unique aud took us quite by surprise. It was a spacious hall called the Grotto saloon, with walls inlaid throughout with every variety of sea shell wrought into various pictures, and with pillar and frieze inlaid with rare minerals and precious stonea. It presented an effect so novel and in some respects so litting as a grotto that we plead guilty to a certain admiration of the room, though it must have been the offápring of a strange caprice originally. We were taken through several rooms all more or lesa richly adorned and with elegant furniture. In the rooms once occupied by Fredorick the Great werehisstudy-table, chairs, and various sniall articles. In the library was his manuscript of the Eloge du Sieur la Mettrie, also the portrait drawn by him of Voltaire, then his guest, and which appears to have been alikonesssomewhat of the burlesque order. The theater was quite a beautiful hall, largo enough to contain 500 or 600, and as in all these royal private theaters arranged with seats graded according to certain rules of i cedeuce. The ballroomcontaiuedsevoral good pictures and the decorations were I very fine. The extensivo tnarble saloon ' over 100 feet long, entirely lined with highly poli&h marble, presented an i posing appearanoe of richness, but except when gay with splandid equipage and dazzling with courtly array has a i what cold and coiufortless aspect. The floors of these palaces, inlaid wil h various l native woods waxed and polished to the ' last extreme of slipperyness, always command our admiration. Extending our walk in a southoast direction nearly a mile, through the ever beautiful park, we reached Charlottenhof, the late residence of the King, when Crown Prince, a very unpretending and quiet place. Just . hind it is constructed an open bath house with surrounding pórtico after the anoieut Roman style. Nearly an equal distance northwest froni this we carne upon the Japanese house, an octagonal edifice with fourporchessupportedby columns, at the foot of which were grouped Japanese figures in costume, of no very artistic excellence, but whicheemed to be about the only thing suggesting the appropriateness of the name given to the queer lookng edifice. The interior was a single room following the shape of the exterior and without contents apparently. The frieze extending around this room has a fresco of vines with flowers and apes in;prmingled, from which circumstance Frederick the Great named it with equal fitness his ape saUon. The fountain near by with the figure of Neptune and his sea horses, designed by Kiss, seemedto be nadequate to contain so large a team and .ost much of its beauty thereby. Having thus disposed of the south portion of the Park we recrossed the avenue ust in time to witness the great fountain in play. It consists of but a single large stream shooting upward to a height of 100 feet, and falling back in spray into a noble basin of about 100 feet diameter. Whita #&ted here and moralizing upon the great inconvenience of having fouud one of the royal household in temporary occupancy of Sans Souci, and thus being excluded from admission to its historical halls, the Eoyal Princess, wife of the Crown Prince and daughter of Queen Victoria, passed by in her modest private carriage. The ground from the great fountain rapidly ascends and is laid off in several terraces, up which directly to tha palace a broad flight of steps extend, and near the upper end of these steps are interred the hounds and horses of the whimsical Froderick, There ig nothing in the exterior of the palace worth noting, but its surroundings are of the most attractive kind so far as beautiful trees and shrubbery aud flowers can be made subservient to royal pleasures. Farther west, upon the same level as the Sans Souci, is the Orangerie, a later erection in the Florentine style, occupying a beautiful open and elevatod site, fronting upon a terrace, adorned with several groups of statuary after ancient originals( among which is a very fine bronze oopy of the celebrated Farnese Buil at Naples. The building contains a saloon in which are forty admirable copies of some of the best productions of Eaphael. The oopies of the frescoes in the Vatican were the least satisfactory, being upon a scale considerably smaller than the origináis. We were conducted through the adjoining suite of rooms, very tastefully furnished auH containiug some interesting objects of art and furniture. These rooms had been occupied by Prince Hurubert and the Princes Marguerita during their visit to Berlin last season. The grounds upon the sloping hillside are adorned with frequent statues and other sculptures and seem to be thrown open without restriction to the public. Only a few rods east of the Sans Souci, very conspicuous and erect and showing no signs of surrender, stills stands the old Windmill which Frederick the Great had not tnoney enough to buy, still the property of the same family which refused to sell it a century ago, and proudly pointed at as au evidence of the sacredness of private property in Germany, even where the King's desires are to be frustrated. We could not but gaze with respect upon this venerable object which had unconsciously established the King's virtue though it proved also a subject's obstinacy. We extended our excursión through a fornst-clad hill lying north of the windmill nearly a mile, upon whose top is erected a very natural artificial ruin, consisting of a tower about 75 feet high, a brokeu archway, and several columns standing and fallen. The reservoir into which water is forced by steam is situated at this point and supplies the fountains of the royal park and gardens. It was Tantalus like to be told by the wierd lookitig janitress of this wealth of water, that we could get nothing at her preinises wherewith to quench our thirst. Upon our return to the depot we took the old Garrison Church in our way, and stopped to look into the vault bsneath th e pulpit which contains the remains of Frederick the Great and of Frederick William I. his father. Both coffins are quite plain and appear much alike ; but that of the father is of reddish colored marble while that of the more celebrated son is only of zinc painted of a similar color. We were told by the sacristán that this was accordiug to his own wish. There were no epitaphs or inscriptions laudatory of the noble dead, nor even any record of the sacrilegio appropriation of the sword of the great Frederiek by the great Xapoleon when visiting this tovu. Some com pensation it must be cpnfessed is to be found in the fact that ainong the trophy flags suspended at each side of the pulpit are a nuruber captured from the French in 1813-15, The uniforma worn by tho three allied sovereigns in the campaign of 1813 are said to be preserved in this church but we did ïiot see them. It -was certainly a very enjoyable excursión wo had that day at Potsdara, and it is placed among our most agreeablereminisccrices of travel. It is singular how conjpleteiy the the national uiind and iiistitutions ara perineated and influenoed by the superior prominenoe often times of a single individual. At Paris on every hand wpre to be seen the hand and work of Napcleon ; here in Berlin everytliing is associated with the name ot' Frederiek the Great : churche9, palaces, theaters, bridgeswereof his coustruction, and inouiiments,statues,aud statuettes and portraits abound in public and privuto uluces alike. However mueh we have been disappointed in some respects with Berhn there is a large balance of attractions in its favor, and those who have made the longest stay are genorally bost ploased with the city. That it is yet a growing place and is destined, with a continuance of the empire, to become the vast center of all the great national impulses and activities, still it occupies a site quite destitute of natural beauty and must créate in this respect whatüver of attractiveness it raay over present. In palaces and publio buildings it ahounds, though not of any great architectural nierit or adherence to approved styles. In its display of monument in bronze it is exceedingly rich and much fine sculpture is to be seen upon the facades and arrayed along the balustrades of many of its public edifi.es and biidges, but in fine fountains, woll-shaded parks, and avenues for the constant enjoyment of citizen and stranger, the city, within its proper limits, is really quito poor. Had that capacious and too much Depraised Street, " Unter den Linden," been finely shaded with really grand old treas and well provided with seats, along its central passage fur iedostriiins, and in addition had ihe architecture upon either side corresponded with the pretensions and pos3Íbilities cf the streët, it would have been the just pride of the city and made the absence of sm;ill parks less noticable. We left Berlin forDresden upon a very hot afternoon, and it was a great satisfaction to fiud ourselves whiiling along in the comruodious Gorman carsand brea'.hing the fresher and more invigorating air of the country. In a región so raoontonous as that about Berlin there is littlo tobe seen upon the passage, o.tcopt the productions and agricultura! appsarance of the country. We should have much liked to stop off at Jutterbogk, to take a look at one of thosa indulgencies disfri. buted by Tetzol, which is preserved in the church there and which stirred up Luther's pious wrath to such ah extent and "kept it warm," and then take a run of about nu hour to Wittembnrg. wueie his ninety-five theses were posted in 1517, and where he was once an A-iijfüstine monkandthenthegie.it Eefoniio ; but one cannot see everytliing in this land so full of intei-est on evary side. As we approached nearer Dresden tho country became more varied and vtBéyarda uppeir ■ ed on the hill sides, and jibunt sundonn we landed at Nieustarlt, DrcSden, on the North side of the Elbe. Ever yours, J. M, WHEELEE.