or v v F; from 1868-77 it was again p B. It deserves attention.

In Vol. III. of the Moscow Observations, Professor Bredichin has given his observations to determine the parallax of the nebula H iv. 37. The series extended over sixty-five nights, and comprised eight measures of Ad on each night. The observations are grouped into twelve groups. The parallax resulting is 0.065" ± 0.040". This includes the temperature correction of the screw. If the mean value of the screw be used without such correction, the parallax results as 0.009"±0.041". Thus this nebula appears to be at the same distance as the (single) comparison star.

Dr. Dreyer has published his supplement to the "General Catalogue of Nebula and Clusters of Stars" (Herschel). It contains, first, notes and corrections to the catalogue; and, second, a continuation of this. The numbering is continued from 5079 (Herschel's highest number) to 6251. Of course this sum includes errors, duplicates, possible comets, etc., and on this account it has been doubted whether the time for the systematic catalogue of Herschel had come in 1864. The immense convenience of it as a printed working-list quite overbears any possible want of logical arrangement; and Dr. Dreyer's work is a much-needed supplement, and is edited with great care.

Dr. Doberck has given in Nature (February 14, 1878) an abstract of D'Arrest's Undersogelse on spectra of nebulous stars, which will be valuable to English readers, the original paper being almost unknown. About 6000 nebula were known in 1872; of these 150 have been examined with the spectroscope-only one-fortieth part. Of these about three fourths give the continuous spectrum, while only one fourth are true gaseous nebulæ. Gaseous nebula are, with few exceptions, characterized by greenish-blue light, sharply defined circular or elliptic disks, and often have bright condensations within, almost stellar in appearance. A few are, however, large, irregular, and complicated, like nebula Orionis, for example. The ray-like elongated nebula are, so far, always characterized by a continuous spectrum. The characteristic lines of a gaseous nebula have the wave-lengths, according to D'Arrest, (A) 5004.0, (B) 4956.6, and (C) 4860.6, with a fourth line occasionally present. From a great number of

observations, Bredichin gives these: (A) 5003.9 ± 1.2, (B) 4957.9±11.4, (C) 4859.2±3.1.

Professor Holden has made a determination of the relative brightness of the different parts of the nebula of Orion, and for this purpose has used a photometer devised by Dr. Hastings, of the Johns-Hopkins University. These photometric determinations show that this instrument is capable of giving excellent results.

Dr. Vogel, of the Potsdam Observatory, has published the results of measures on the cluster x Persei, made in 1867-70 by means of the 8-inch refractor at Leipsic, with the object of fixing the relative positions (and magnitudes) of the stars of this cluster, so that any future change may not pass undetected. 176 stars, in all, have been fixed in position by the filar micrometer. The field was bright, and a magnifying power of 145 diameters was employed throughout. The various sections of this work of 36 quarto pages treat of the following subjects:

§ 1. The position of the instrument; the determination of the parallel.

§ 2 contains an investigation of the position-circle, and of the value of the revolution of the micrometer. The zero of the micrometer is dependent upon the position of the instrument, and also upon the kind of illumination of the thread. The value of the revolution is found from transits on twenty nights, from November, 1867, to May, 1870. During all this time the reticle was left at the same distance from the objective, and the thermometric coefficient resulted +0.001581′′ t° in Réaumur's scale. The magnitude and the sign of this Dr. Vogel explains by the fact that the focal point was not determined each night (as he says is usual), and he correctly points out the necessity of leaving the focus unchanged for such observations, and for determining the value of the screw during the series itself.

§ 3 deals with the methods of observation and reduction. The brighter stars less than 10 magnitude were determined from measures of p and s with four selected stars of the group. These four were connected by measures of p and s and also ▲a and Ad; and they were further connected with two stars of the cluster h Persei, which had been observed with the Bonn meridian-circle. For each pair of the brighter

stars at least four nights' observations were made. The reductions are complete, and the observations are reduced to 1870.0.

The fainter stars (10-12 mag.) were observed by ▲a and Ad with other stars at least on two nights for each star.

§ 4 deals with the accuracy of the observations, and first, for the brighter stars, the probable error of a single observation in s is found to be 0.228", in p (reduced) ± 0.306". The probable errors for the mean of each night are more important, and result as follows (no dependence of the probable errors on the distance or the position-angles being evident): probable error of one night in s, ±0.190", in p (reduced) ±0.165". For the final position (at least four nights) these become, in s, ±0.092"; in p, 0.080". For the Aa and Ad of the brighter stars these are ±0.097" in R. A., ±.089" in N. P. D. The positions for the fainter stars are determined within less than 1" in each co-ordinate, which Dr. Vogel considers sufficient for his purpose.

§ 5 treats of the determinations of the brightness of the stars of this cluster. The 176 stars of the cluster range between the 6.5 and 13 magnitudes.

Each one of the fainter stars (higher than 10 mag.) was determined by eye estimates of magnitude at least five times; the probable error of the mean is ±0.14 magnitude. The brighter stars were determined on several evenings by the eye, and on two nights each was compared by a Zollner photometer with one of the standard stars. A table (p. 12) gives the magnitudes of the brighter stars, 1st, by eye (Vogel); 2d, by eye (Argelander); 3d, photometric magnitude, assuming the light ratio, or 0.397. The agreement is remarkable, but the table shows (what was already known) that Argelander's magnitudes higher than 9.0m make the stars too bright.

§ 6 gives the observations of the stars (in tabular form), and the results. A difference between the spring and autumn observations, in both Aa and Ad, of one of the stars indicates possibly a parallax of about 0.3".

§ 7 gives the observations of the fundamental stars, and catalogue of the 30 brightest stars. The observations are of relative ▲a and Ad of the four fundamental stars, and of two of Argelander's stars in h Persei, and also meridian observa

tions. These last also indicate a parallax to the star b. None of the stars appear to have a large proper motion.

§ 8 deals in the same way with observations of the fainter stars, and catalogue of all the stars of the cluster. This is followed by two charts, one of the brighter stars and the plan of triangulation, the other of the whole cluster.

This brief analysis will give an idea of the contents of this extremely thorough paper, which will take its place beside the other researches of the author in the same field. They are all models of what such investigations should be, and leave nothing to be desired in methods of observation or reduction, in the accuracy of the final results reached (which are always adequate to the purpose in hand), and, finally, are excellent examples of the literary style and clearness appropriate to such memoirs.

NEW STARS; VARIABLE STARS; RED STARS; PROPER MOTIONS, ETC.

Dr. Fearnley, Director of the Christiania Observatory, states that a ninth-magnitude star, a=11h 13m 31, d=+66° 31′ 25′′ (1875), has a proper motion of 3.04" in a great circle, as shown by a comparison of his observations with the Bonn observations of 1855. This star is 60° distant from the solar apex, and the direction of its motion is such as to indicate that we have really to do with a star near to us, and therefore suitable for observation for parallax.

"The Red Stars: Observations and Catalogue," is the title. of a work by J. Birmingham, published in the Transactions of the Royal Irish Academy, Vol. XXVI., Part 7. It includes all known red or yellowish-red stars, 658 in number, with the positions given for 1880. The catalogue gives the magnitudes (mostly from Argelander) and details concerning the color, brightness, and variability, together with an account of spectroscopic observations. Birmingham's observations have been made with a telescope of 4.5 inches aperture, with a power of 53 diameters; and with this instrument stars to the tenth magnitude can be observed, and their color determined. Such an aperture has for its minimum visibile 12.5 magnitude on Argelander's scale. The observations lead to the conclusion that for variable red stars the red color in general is increased with a decreasing magnitude. His explana

tion of this is that the star may be surrounded by a rotating nebulous ring of different thickness at various parts, so that variations of both color and intensity are the results of absorption.

DOUBLE, BINARY, AND MULTIPLE STARS.

Mr. Burnham, of Chicago, has published his ninth catalogue of new double stars discovered with the 6-inch refractor. It comprises the discoveries of 1876 and the first part of 1877. It contains Nos. 453-482, i. e. thirty stars; of these, eighteen are closer than 2.11".

No. 4 of the publications of the Cincinnati Observatory for 1877 has been received. It gives the measures of 517 double stars. The introduction contains an account of the methods of observing. Positions are measured by placing the objects between parallel wires, and with both forward and backward motions of the tangent screw and distances, so as to eliminate the zero and to make the bisections symmetrical. The three observers were found to have a personal equation in position-angle, which Professor Stone refers primarily to the position of the observer's head. The observations are compared with older series, and the probable errors determined. The colors are noted on a new plan, by using numbers, which allow them to be expressed briefly.

This publication of the detailed observations is followed. by a volume of Mean Results, which is a summary of the preceding work. It is in octavo form, sixty stars on a page, and contains observations on 517 such pairs of stars. On the average, about two observations have been made on each pair, both in position and distance. The various columns have for caption, " Number," "Name," "Epoch," "PositionAngle," "Distance," and "No. of Obs." Many close pairs have been measured, and also many neglected stars are to be found in the list.

The Rendiconti of the (Italian) Royal Academy of Sciences for May, 1877, contains a memoir by Signor A. Nobile on the trapezium of Orion (748). The instrument employed was a refractor of 0.14m (5.51 inches) aperture. The method of observation employed was that invented by Nobile, and previously described by him. We possess previous determinations of the relative positions of these stars by W. Struve