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The nature of variable stars
246
Book
REVIEWS.
[J. I;. I.
periodical, and patent literature. There is also material presented which has not been discussed in prior literature. The method of presentation enables the book to be of great assistance to anyone whose interests lie in this direction. R. H. OPPERMANN. ThE NATURE OF VARIABLESTARS, by Paul W. Merrill, I34 pages, plates, illustrations, 14 X 2I cms. New York, The Macmillan Co., 1938. Price $2.oo. The ever-increasing number of large telescopes, and their great achievements, has tended to overshadow completely the small instruments in the hands of amateur astronomers. But there is still a vast field for the little fellows. There is work which they can do quite efficiently and for which, therefore, it would be most uneconomical to employ the more powerful artillery. This is especially true of observations of variable stars, and the work of the American Association of Variable Star Observers, generally known as the AAVSO, consisting almost entirely of amateurs, is going far to solve the problems concerned with these numerous stars that vary more or less regularly in brilliance. In producing a small elementary book devoted to these objects, Dr. Merrill, a distinguished member of the staff of the Mt. Wilson Observatory has filled a very definite need, and it may have the useful function of attracting new workers to this field. Thousands of amateur telescopes could be put to good use in this way. But Dr. Merrill's book is not a handbook for the observer, amateur or professional. It is a clearly written account of present-clay ideas. Few technical terms are used; when it is necessary to introduce them, they are fully explained. Many persons who have read one or more of the numerous excellent books on popular astronomy published in the last few years will find it of interest as dealing with one important phase of astronomy in a more detailed manner. And even to one who has not had this introduction, it will, as the author states in the Preface, "help him to understand the sort of thing with which astronomers are occupied, and why their work has so many points of contact with other sciences." Of particular interest to many readers will be his chapter on the "novae," or " n e w " stars, those bodies which suddenly "swell up and burst," in the words of a famous telegram which is quoted. " T h e outflow of light and heat from a star," says Dr. Merrill, " m a y be compared with a stream of water from a reservoir. The behavior of an ordinary star corresponds to the steady flow of water through a pipe of a certain size; of a periodic variable to a pulsating flow caused by a regular rise and fall of the level of water in the reservoir or to some automatic geyser-like action of the outlet system; in a nova, the dam breaks." Just what makes it break is yet to be determined. At present, he admits, we know much more about how a star varies than why. But gradually knowledge is coming, and this knowledge will tell us far more about stellar evolution in general. Therein lies the great importance of the study of variable stars. To one Hke Dr. Merrill, who is working in this very field, the gaps in our knowledge are strikingly apparent, and throughout there is a refreshing lack of dogmatism. " T h e story of our knowledge of stellar evolution is a sad one of small successes and large blunders," he says. His warning against placing too much faith in theoretical conclusions is also worth quoting:
Feb., 1938.]
P U B L I C A T I O N S RECEIVED.
247
" W e can see but a very small fraction of the radius into any star, even a highly tenuous long-period variable. Thus the only portions accessible to direct observation are the extreme outer layers. The only way to learn about the interior is by what Eddington has called an 'analytical boring machine, which is supposed to bore mathematically into the interior and to bring up a sample. T h e trouble is t h a t the drill takes down some of the engineer's ideas and hypotheses and these so color the material brought up t h a t we are a bit uncertain as to its original properties.' Technical journals are filled with elaborate papers on conditions in the interiors of model gaseous spheres, but these discussions have, for the most part, the character of exercises in mathematical physics rather than astronomical investigations, and it is difficult to judge the degree of resemblance between the models and actual stars. Differential equations are like servants in livery: it is honorable to be able to command them, but they are ' y e s ' men, loyally giving support and amplification to the ideas entrusted to them by their master." The plates and the diagrams are well selected, and aid in the explanations. Mechanically, the book is all t h a t could be desired, and two indices, one of stars, the other of subjects, materially add to its usefulness. JAMES STOKLEY. AMERICAN INSTITUTE OF MINING AND METALLURGICAL ENGINEERS, TRANSACTIONS, Vol. 125, Iron and Steel Division. 602 pages, plates, illustrations, tables, 15 X 23 cms. New York, Institute, 1937. Price $5.00. This is the t e n t h of a series confaining papers before the Iron and Steel division of this society. It covers the meetings of October 1936 and February I937, and contains such interesting papers as Dr. P. D. Merica's Memorial Lecture on Progress in Improvement of Cast Iron and Use of Alloys in Iron, a paper on Blast Furnace PractiCe by J; M. Hassler, and the Freezing of Cast Iron by Alfred Boyles. There is a comprehensive index in the back of the volume which adds materially to its value. R. H. OPPERMANN.
PUBLICATIONS RECEIVED. Hydro- and Aero-Dynamics, b y S. L. Green.
185 pages, illustrations, 14 New York, Pitman Publishing Corporation, 1937. Price $3.5o. The Chemistry of Petroleum Derivatives, by Carleton Ellis. Volume II, 1937. 1464 pages, illustrations, 16 >( 23 cms. New York, Reinhold Publishing Corporation. Price $2o.oo. Segmental Functions, Text and Tables, by C. K. Smoley. 435 pages, 12 )< I8 cms. Scranton, C. K. Smoley and Sons, I937. Price $5.oo. X 22 cms.
Etude Pratique des Rayonnements, Solaire, Atmosphdrique et Terrestre (M~.thedes et Rdsultats), par Ch. Maurain. 18o pages, illustrations, tables, 16 X 25 eros. Paris, Gauthier-Villars, 1937-
Price 80 fr.
The Fine Structure of Matter, The Bearing of Recent Work on Crystal Structure, Polarization and Line Spectra, being Volume II of a comprehensive treatise of atomic and molecular structure.
Part I: X-Rays and the Structure of Matter, by
Book
REVIEWS.
[J. I;. I.
periodical, and patent literature. There is also material presented which has not been discussed in prior literature. The method of presentation enables the book to be of great assistance to anyone whose interests lie in this direction. R. H. OPPERMANN. ThE NATURE OF VARIABLESTARS, by Paul W. Merrill, I34 pages, plates, illustrations, 14 X 2I cms. New York, The Macmillan Co., 1938. Price $2.oo. The ever-increasing number of large telescopes, and their great achievements, has tended to overshadow completely the small instruments in the hands of amateur astronomers. But there is still a vast field for the little fellows. There is work which they can do quite efficiently and for which, therefore, it would be most uneconomical to employ the more powerful artillery. This is especially true of observations of variable stars, and the work of the American Association of Variable Star Observers, generally known as the AAVSO, consisting almost entirely of amateurs, is going far to solve the problems concerned with these numerous stars that vary more or less regularly in brilliance. In producing a small elementary book devoted to these objects, Dr. Merrill, a distinguished member of the staff of the Mt. Wilson Observatory has filled a very definite need, and it may have the useful function of attracting new workers to this field. Thousands of amateur telescopes could be put to good use in this way. But Dr. Merrill's book is not a handbook for the observer, amateur or professional. It is a clearly written account of present-clay ideas. Few technical terms are used; when it is necessary to introduce them, they are fully explained. Many persons who have read one or more of the numerous excellent books on popular astronomy published in the last few years will find it of interest as dealing with one important phase of astronomy in a more detailed manner. And even to one who has not had this introduction, it will, as the author states in the Preface, "help him to understand the sort of thing with which astronomers are occupied, and why their work has so many points of contact with other sciences." Of particular interest to many readers will be his chapter on the "novae," or " n e w " stars, those bodies which suddenly "swell up and burst," in the words of a famous telegram which is quoted. " T h e outflow of light and heat from a star," says Dr. Merrill, " m a y be compared with a stream of water from a reservoir. The behavior of an ordinary star corresponds to the steady flow of water through a pipe of a certain size; of a periodic variable to a pulsating flow caused by a regular rise and fall of the level of water in the reservoir or to some automatic geyser-like action of the outlet system; in a nova, the dam breaks." Just what makes it break is yet to be determined. At present, he admits, we know much more about how a star varies than why. But gradually knowledge is coming, and this knowledge will tell us far more about stellar evolution in general. Therein lies the great importance of the study of variable stars. To one Hke Dr. Merrill, who is working in this very field, the gaps in our knowledge are strikingly apparent, and throughout there is a refreshing lack of dogmatism. " T h e story of our knowledge of stellar evolution is a sad one of small successes and large blunders," he says. His warning against placing too much faith in theoretical conclusions is also worth quoting:
Feb., 1938.]
P U B L I C A T I O N S RECEIVED.
247
" W e can see but a very small fraction of the radius into any star, even a highly tenuous long-period variable. Thus the only portions accessible to direct observation are the extreme outer layers. The only way to learn about the interior is by what Eddington has called an 'analytical boring machine, which is supposed to bore mathematically into the interior and to bring up a sample. T h e trouble is t h a t the drill takes down some of the engineer's ideas and hypotheses and these so color the material brought up t h a t we are a bit uncertain as to its original properties.' Technical journals are filled with elaborate papers on conditions in the interiors of model gaseous spheres, but these discussions have, for the most part, the character of exercises in mathematical physics rather than astronomical investigations, and it is difficult to judge the degree of resemblance between the models and actual stars. Differential equations are like servants in livery: it is honorable to be able to command them, but they are ' y e s ' men, loyally giving support and amplification to the ideas entrusted to them by their master." The plates and the diagrams are well selected, and aid in the explanations. Mechanically, the book is all t h a t could be desired, and two indices, one of stars, the other of subjects, materially add to its usefulness. JAMES STOKLEY. AMERICAN INSTITUTE OF MINING AND METALLURGICAL ENGINEERS, TRANSACTIONS, Vol. 125, Iron and Steel Division. 602 pages, plates, illustrations, tables, 15 X 23 cms. New York, Institute, 1937. Price $5.00. This is the t e n t h of a series confaining papers before the Iron and Steel division of this society. It covers the meetings of October 1936 and February I937, and contains such interesting papers as Dr. P. D. Merica's Memorial Lecture on Progress in Improvement of Cast Iron and Use of Alloys in Iron, a paper on Blast Furnace PractiCe by J; M. Hassler, and the Freezing of Cast Iron by Alfred Boyles. There is a comprehensive index in the back of the volume which adds materially to its value. R. H. OPPERMANN.
PUBLICATIONS RECEIVED. Hydro- and Aero-Dynamics, b y S. L. Green.
185 pages, illustrations, 14 New York, Pitman Publishing Corporation, 1937. Price $3.5o. The Chemistry of Petroleum Derivatives, by Carleton Ellis. Volume II, 1937. 1464 pages, illustrations, 16 >( 23 cms. New York, Reinhold Publishing Corporation. Price $2o.oo. Segmental Functions, Text and Tables, by C. K. Smoley. 435 pages, 12 )< I8 cms. Scranton, C. K. Smoley and Sons, I937. Price $5.oo. X 22 cms.
Etude Pratique des Rayonnements, Solaire, Atmosphdrique et Terrestre (M~.thedes et Rdsultats), par Ch. Maurain. 18o pages, illustrations, tables, 16 X 25 eros. Paris, Gauthier-Villars, 1937-
Price 80 fr.
The Fine Structure of Matter, The Bearing of Recent Work on Crystal Structure, Polarization and Line Spectra, being Volume II of a comprehensive treatise of atomic and molecular structure.
Part I: X-Rays and the Structure of Matter, by