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On the whole, the book is a valuable addition to our meagre collection of text-books on the new system, and we commend it to the notice of teachers.

2. Van Nostrands Eclectic Engineering Magazine. 80 to 96 pp. large 8vo. Monthly: vol. I, No. 1. Jan. 1, 1869.—This periodical meets a want which must have been generally felt by American Engineers, of a magazine that should furnish abstracts of important investigations, and of the expositions of new projects, valuable experimental results, and signal achievements in works of construction, that may appear in the Engineering serial publications of Europe and America. It is designed to provide the American Engineer with the means of readily informing himself with regard to the "current fact and opinion" in his profession both at home and abroad; and is calculated to prove a valuable aid in this way, and by furnishing an index to important discussions, even to those who may have the leisure to consult the original publications.

The work of selection and condensation from other Journals, and of editing, generally, this new Magazine, is under the able direction of Mr. A. L. Holley, the well known author of valuable Engineering works, and practical Engineer. Two numbers have been issued, and they must be pronounced a decided success. They afford good indication that the design set forth in the Publisher's Prospectus of presenting "within limits of space and cost that all can afford,” the cream of all the principal Journals of Practical Science, will be satisfactorily realized.

3. Annual Report of the Board of Regents of the Smithsonian Institution, showing the operations, expenditures and condition of the Institution for the year 1867. 506 pp. 8vo. Prof. Henry adds very greatly to the scientific value of his reports, by the various memoirs which are appended. In the present volume there are biographical sketches of Legendre, Peltier, Faraday and the Jussieus; a paper on the natural history of organized bodies, by M. Marey; on the electrical currents of the earth, by C. Matteucci; on Man as the cotemporary of the Mammoth and the Reindeer in Middle Europe, from the German “ Aus der Natur;" Photo-chemistry, by Jamin; on Traces of the early mental condition of man, by E. B. Taylor; besides various other articles in Ethnology, Geography, Zoology, Meteorology, Physics, etc.

4. The Manufacturer and Builder: a Practical Journal of Industrial Progress. Western & Company, Publishers, 37 Park Row, New York. January, March, 1869." This new serial commenced with the current year, appears monthly, at the very low price of $1.50 for the year. It is beautifully printed in a large quarto form, of three columns, on excellent paper, and will prove to be an important addition to the resources of the large class of practical men, to whose interests it is exclusively devoted. Its success is already assured by a very large circulation.

5. Blank Maps for marking the distribution of Plants and Animals.-The Boston Society of Natural History has issued blank maps, designed for marking, by pencil or water-colors, the limits of known distribution of given species of animals or plants over the area delineated. Since, for such a purpose, the student needs a larger or smaller number of charts, according as his field of research is wider or narrower, they have been prepared, a circular states, as cheaply as possible, consistent with entire accuracy. They have been purposely printed on thin paper, which will take water-colors, and will be furnished in any number at the cost price of a very large edition, viz: $6.70 per hundred. Copies are ready for delivery, and can be obtained by forwarding the necessary sum to Samuel H. Scudder, the Librarian of the Society.

6. Le Naturaliste Canadien.-A popular scientific monthly in French, of the above title, has been commenced at Quebec under the editorial charge of M. L'ABBE PROVANCHER, curé de Portneuf. Each number contains 24 pages 8vo, and the first was published in December last.

Report of the British Association for the Advancement of Science for 1867. 522 and 196 pp. 8vo. London, 1868. (John Murray).

Contributions to the Fauna of the Gulf Stream at great depths; by L. F. de Pourtales, 1st series, 1867, 2d series, 1868. Bulletin of the Museum of Compar. ative Zoology, Cambridge, Mass.

Catalogue of the Orthoptera of North America described previous to 1867. By Samuel H. Scudder. 89 pp. octavo, 1868.-Smithsonian Miscellaneous Collections.

On the Origin of Genera. By Edward D. Cope, A. M. 80 pp. octavo, 1869. From the Proceedings of the Acad. Nat. Sci. Philadelphia.

PROCEEDINGS OF THE ESSEX INSTITUTE, Salem, Mass. Vol. v, No. 8.—p. 188, Progress of Sacred Music in New England; A. C. Goodell, Jr.-p. 191, American Lichenography; H. Willey.- COMMUNICATIONS.—p. 273, List of the Birds of New England; E Coues.-p. 315, Synopsis of the Polyps and Corals of the North Pacific Exploring Expedition, Part 4, Actinaria; A. E. Verrill.

ANNALS LYC. Nat. Hist. of New YORK. Vol. ix, Nos. 1-4, April, 1868-p. 1, Notes on the Later Extinct Floras of North America, with Descriptions of some New Species of Fossil Plants from the Cretaceous and Tertiary Strata; J. S. Newberry.- p. 76, Notes on certain Terrestrial Mollusca, with Descriptions of New Species; T. Bland.-p. 86Catalogue of the Birds found in Costa Rica; G. N. Lawrence.

PROCEEDINGS OF THE AMERICAN PHILOSOPHICAL Soc. Vol. x, No. 80, Oct. to Dec., 1868.-p. 445, Notes on the Origin of Bitumens, together with Experiments upon the formation of Asphaltum; S. F. Peckham.-p. 463, Notes on the Geology of Wyoming and Colorado Territories; F. V. Hayden.-P. 481, Obituary Notice of W. P. Foulke; J. P. Lesley.-P. 513, Obituary Notice of J. R. Ingersoll; G. Sharswood.-p. 522, Indian Figures cut on rocks; T. C. Porter.-p. 523, Tidal Rainfall at Philadelphia, P. E. Chase.-p. 539, Observations on the Meteors of Nov. 14; P. E. Chase.-P. 541, On the Shower of November Meteors; D. Kirkwood.-p. 543, Notes on the D'Orbinay Papyrus; J. P. Lesley.-P. 561, Classified Catalogue of the Harris Collection in Alexandria, Egypt; J. P. Lesley.

PROCEEDINGS Bost. Soc. Nat. Hist. Vol. xii.-p. 162, Description of a New Species of Thecla; C. P. Whitney —p. 165, Descriptions of American Bees, No. 1, Andrenidæ; E. T. Cresson.-p. 171, Catalogue of the Reptiles and Batrachians found in the Vicinity of Springfield, Mass.; J. A. Alen.-p. 205, Some Observations on the Fauna of Madeira; F. H. Brown.-p. 214, Sketch of the Life of Dr. Ebenezer Emmons; J. B. Perrey.—p. 219, Indian Relics at Swanton, Vt.; J. B. Perrey.-P. 222, Geographical Distribution of the Birds of the Department of Vera Cruz; F. Sumichrast.—225, Vision of Fishes and Amphibians; B. J. Jeffries. -p. 228, Arrangement of the families of Orthoptera; S. H. Scudder.-P. 235, On the Landslides in the Vicinity of Portland, Me.; E. S. Morse.—p. 244, Obituary of John Cassin ; T. M. Brewer.—p. 248, Additional Notes on the Reptiles and Batrachians of Springfield, Mass.; J. A. Allen.-p. 250, On the Reptilian Orders, Pythonomorpha and Streptosauria; E. D. Cope.





Art. XXV.-On the Variability of Personal Equation in

Transit Observations; by WILLIAM A. ROGERS, Director of Alfred University Observatory. The personal equation of an observer is the interval of time which habitually intervenes between the actual and the observed transit of a star over a given thread of the transit instrument. This may be termed the absolute personal equation.

The relative personal equation of two observers is the interval of time by which one habitually observes a transit either earlier or later than the other; or, it is the difference between their absolute equations.

It is well known that personal equation is one of the most iincertain elements in chronographic determinations of longitude. It has been the custom, at least in this country, in observations for longitude, to assume that the value of this function of the time remains unchanged during the entire series, even though the comparisons for the determination of this element were delayed for several weeks. Now if the personal equation of the observers is not a constant quantity, if it can be shown that from any cause it varies from week to week, from day to day, and even from hour to hour, between limits nearly as large as the usual value of the function itself, it will be evident that some uncertainty yet remains in the accepted values of longitude, especially since in almost every instance, the observations for longitude and personal equation have been separated by a considerable interval of time. The investigation of the variability of personal equation is, therefore, not an idle inquiry.


The results on which this discussion is founded depend upon about 8,000 observations of artificial stars. In the present instance, the artificial stars were made of paper and centered upon fine steel wires placed in a vertical position. Now it is evident that if the wire to which the star is attached, could be made to pass a stationary vertical wire with a uniform motion, and if the exact time of opposition could be automatically recorded, we should have a standard with which the observed time of passage could be compared. The following device was employed to accomplish this object.

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Let Q Q in the figure represent the cylinder of a Bond chronograph. At one end of the cylinder and attached to the table upon which the chronograph rests, is placed a wire frame work ABCDEF, in such a position that the vertical face BCDE shall be parallel with the plane of the end of the cylinder and in close proximity to it. ee', oo' are two vertical threads of fine wire. aa', bb', cc', are fine steel wires placed vertically at the circumference of the base Q. Upon these wires are centered the stars 8 8' 8". ii' is a wire insulated with respect to the frame work at i and i' but in contact with it at z. To the end of this wire is attached a fine needle i" ;'"' projecting beyond the plane of the wires on the cylinder just far enough to come in contact with them as they revolve. The wires w w' run to a battery after passing through a coil (not represented in the figure) with which the pen p p' is connected.

As the cylinder revolves, the instant b b' arrives opposite e e' it breaks the connection at a and the circuit continues broken till the needle springs back upon ee'. During this interval a spring attached to pp' moves it horizontally, making a break at m. The beginning of the break is the instant of opposition. At another revolution another break is made at m',

and we thus have the instant of opposition automatically recorded upon the line mm''. Suppose an observer standing at X with a break-circuit key, to observe through a small telescope, the instant of conjunction between the fixed wire o o' and the movable one bb'. By breaking the circuit at that instant, a break is made at n, depending only on the judgment of the observer. Now, if the measured interval between the two fixed wires e e' and o o' is

equal to the interval between m and n, expressed in the same unit, there is no absolute personal equation. If mn is less than z z' the observation is too early, if greater, it is too late, in either case by the difference between zz' and mn.

In order to find the common unit of measurement, the galvanic connection is made through the clock; then every alternate swing of the pendulum gives the constant spaces ur, U' r', u" ", each equal to two seconds of time. In the present instance this space was divided upon mica into twenty equal parts by the aid of a filar micrometer screw. By placing the scale upon mn,

the distance from m to n is measurable to 1s and by estimation to .01s. The value of zz' adopted in this discussion after numerous and careful measurements upon different parts of the scale, is 773+.0159. Hence whenever the interval between the beginning of the automatic break and that made by the observer is less than 778 the observation is too early, and when greater, it is too late. The difference, either way, is the absolute personal equation. If there are two observers, their relative personal equation is easily found, from the absolute equation of each,

In entering upon this discussion the first and the main question is :

Does the personal equation vary from any cause ? As the basis of investigation, I give below the mean of the values found for each date, with explanatory remarks concerning the conditions under which the observations were made. By an abnormal position of the body, I mean as painful a position as I could assume. The wires were illuminated by placing a light nearly in front of them. Faint illumination was produced by reducing the volume of the flame.

The observations were made by Prof. Edward M. Tomlinson, Mr. Herbert E. Babcock, and myself.

Absolute Personal Equation.

Date. Equation.

Date. Equation.

Remarks 1867.

1867. Nov.

Nov. 19=-1188

29 +:017—Read up all the preceding 20 093

records. 21 057-Read the record for Nov. 19 Dec. 22 ·022 and 20. First knowledge of 5 - 067 Normal position. 23 088 the value of my personal 5 •032 Abnormal position. 24 - 047 equation. Observations from 0 .038 Normal. 25 +.025 Nov. 19 to Nov. 29 werel 6 •037 Abnormal. 26 .019 made under a normal condi- 7 .042 Normal. 27 ·034 tion of the body.

7 ·040 Abuormal. 28 019

8 042 Normal.

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