Lohrmann's Lunar Map

From Wikisource
Jump to navigation Jump to search

Lohrmann’s Lunar Map. Mondkarte in 25 Sectionen von W. G. Lohrmann, mit beschreibendem Text von Dr. J. F. Julius Schmidt. Verlag Von J. A. Barth in Leipsig. Price 50s.

A desideraturn long awaited by astronomers has been at length supplied by the publication of Lohrmann's complete map of the moon. The first part of his Topographie, &c., which contained only four sections of the twenty-five composing the map, was published so long ago as 1824, and no more of this great work was issued; but in 1838 a small map, comprising all the sections on a reduced scale, was lithographed by Werner at Dresden.

Lohrmann’s lunar survey commenced in Dresden in 1821, and was finished in 1836. In 1840 he died, and Mädler, in the mean time, having stepped into the field, the work of the other fell for a period into neglect; but, fortunately, his manuscripts were in the hands of a true lover of science — Herr W. A. Barth, of Leipsig — who, at his private cost, undertook their publication according to the original plan of the author. In this he was assisted by Herr Opelt of Dresden, who revised the calculations and the tables, and superintended the engraving. The work, however, proceeding but_slowly, Herr Barth, in February 1851, applied for the assistance of Dr. Schmidt, of the Athens observatory. Though Dr. Schmidt was at the time fully engaged with his own lunar map, he willingly responded to the call, and the work was quickly progressing when Herr Barth died in December of the same year. It was now fortunate that his son, Dr. A. A. Barth, determined to carry out the wishes of his father; and, after a lapse of two years, Dr. Schmidt resumed his labours at the map. Dr. Schmidt got his appointment as Director of the observatory at Athens in 1858; and the work then chiefly fell on Opelt, who was assisted by his son, a First-Lieutenant in the Saxon army; and the task was continued by the latter, after the death of his father in 1863.

Another death now occurred which might have been fatal to the final success of the undertaking, namely, the death of Dr. A. A. Barth, were it not that he was succeeded by a man of equal zeal in the cause of science, Herr J. A. Barth, who was determined to accomplish the design of his predecessors, and Lohrmann’s 25 Sections have, accordingly, at length appeared with a descriptive_letterpress written by Dr. Schmidt, who also completed the final revision and correction of the tables.

The map of 3 French feet, measures the 3 1/2 millionth of the moon’s diameter. The new text, by Schmidt, is on a considerably abridged plan compared with Lohrmann’s. The parts connected with general astronomy are omitted; so also are the biographical notes relating to lunar nomenclature, and the method of calculating and fixing positions. On the other hand, Lohrmann’s account of his mode of delineation is retained, and a list of positions by Opelt is added. Lohrmann’s minute descriptions are also modified, as Dr. Schmidt considers that the various minor objects are sufficiently well outlined on the map, and require no special reference in the text.

In the preface to the published part of his work Lohrmann explained that his design was to represent the lunar mountains and shadings as closely as possible; and, following the methods of measuring and representation as prescribed by science, he adopted the orthographic projection of the lunar surface seen at mean libration.

As might be naturally expected, in a work of engraving taken in hand at intervals during a space of fifty years, a very unequal style of performance in the different plates was the result, and the several tones of shading, which even in the Lohrmann’s originals were not always satisfactory, appeared in very different proportions in different parts of the map.

To correct these completely would involve too much labour and expense, but some of the most important features have been retouched by Dr. Schmidt, who also has struck out several names that impaired the clearness of delineation.

To the largely increasing class of astronomers, professional and amateur, who make the lunar surface their study, and who have depended hitherto chiefly on Beer and Mädler’s map, the publication of Lohrmann’s complete sections must be highly appreciated. Schmidt's own wonderful map of 6 feet diameter will soon appear, and then we shall have the opportunity of testing our own observations by comparison with the lunar features as represented in no less than three great works. Evidences of continued volcanic activity in the moon may now be sought with increased facility, while at the same time, the almost cotemporary maps of Lohrmann, and B. and M. may serve to show that many apparent differences are due to the mode, or accidents of sketching rather than to change.

Too much praise cannot be given to Herr J. A. Barth for his liberal expenditure in carrying out the excellent design of his predecessors; and it is to be hoped that the undoubted value of the work will insure a demand that will amply reimburse a large outlay.

The astronomical world must surely recognize the good fortune that placed the task of editing in hands like those of Dr. Schmidt, whose disinterested conduct in suspending his labours at his own map for the purpose of publishing the work of another, and giving it precedence, is quite in keeping with the estimable character and scientific devotedness of the chief of the Athens observatory.