The Museum Environment was immediately accepted as the standard reference on preventative conservation within the museum community upon its publication in 1978. It was the first attempt to comprehensively treat this subject in a single volume. Now, after nine years, we have a second edition of this authoritative text, which incorporates a number of changes. While these modifications present some useful additional information, the major reason for applauding the appearance of this second edition is the renewed availability of The Museum Environment which had been unavailable for over a year.

A few sections have been rewritten and a few new sections have been added, and most of these changes represent updatings of research and recommendations that had been published after the appearance of the first edition. The theoretical and explanatory aspects of the book are prepeated almost without revision. From the perspective of this reviewer, this is because the excellent and thorough job that the author did in his first edition required no significant rewriting.

The Museum Environment is meant to serve several audiences and a variety of purposes. As such, it is written in two parts. The first part is intended as a basic introduction to the subject, supplemented by specific recommendations. It is directed to conservators as well as museum specialists not in conservation. The second part summarizes much of the pertinent theory and literature that underpins the first part of the book. Within each part, the museum environment is categorized into three subjects: light, humidity, and air pollution.

Since the original volume has been available for almost a decade, a review of the second edition affords the opportunity to discuss how the book has been received and used to date, as well as to consider the usefulness of the revisions found in the second edition. Prior to its initial publication, no single book dealt comprehensively with information on environmental considerations primarily for museums. Most of the published works that formed a basis for this text were scattered through hundreds of journal articles, or were unwritten but common practice within parts of the profession. While the conservation profession had acknowledged the importance of environmental control for many years, the basic knowledge remained esoteric and not easily accessible to many practicing conservators. However, with the increased opportunity for academic training in conservation, the surge of interest in museology around the world accompanied by the construction of many new museums, and a new concern for preservation and ecology in its broadest sense, the times had changed. We were ready for Thomson's tome.

Many museum specialists were familiar with the environmental recommendations summarized in The Museum Environment. However, few were conversant with all the reasons and the full background for these values. As a result, many museums chose to ignore or only minimally accept the recommendations for relative humidity, temperature, and air pollution control. Fortunately, the publication of Thomson's work helped give greater authority to these specifications, and assisted many conservators in convincing other museum professionals to accept these conditions for display and storage.

The difficulty with the book is that it provides specifications and explanations but falls short as a handbook on how to implement these requirements in a practical manner. However, such a practical handbook was not the author's intention, as stated in the preface to the first edition: “The more general character of this work makes it no less practical, but certainly indicates a bias towards setting up a generalized framework of knowledge from which particular problems can be solved….” The specific, practical, applied solutions must inevitably reside with the reader, not with the author. Herein lies the strength and weakness of the book.

The museum environment as a subject is a catch-all concept for many different areas of knowledge and experience. It is a credit to Thomson's thoroughness and thoughtfulness that he has been able to incorporate such a vast number of concepts into a book that totals approximately 300 pages. As an introductory text that attempts to organize a confusing body of knowledge for the first time, it is an extraordinary and successful effort. However, it is no more than an introduction. Many of the issues covered here in just a few pages merit major publications in their own right. Complex issues such as natural versus artificial light, or choice of air conditioning equipment—topics which have been discussed here briefly—require more thorough review before any practical decisions can be made at the level of implementation. The problem is that architects, museum administrators, and even conservators look to the pages of this book for final and definitive answers.

We are all familiar with situations where environmental values recommended in The Museum Environment have been demanded by conservators without a full understanding of the explanations for the numbers which Thomson provides. Such blind allegiance without proper understanding can lead to inappropriate recommendation and application of these environmental specifications. The specifications should be used as a modifiable set of guidelines that should be appropriately applied to a given situation. The proper choice of specifications must be derived from both theory and the actual circumstances of application. Only a sound knowledge of both aspects can result in a satisfactory compromise between the reality of a given situation and ideal specifications. Thomson provides an excellent theoretical background from which to make such decisions. The reader must provide the balance of the information and draw his or her own conclusions about specifications in each unique circumstance.

In essence, the strength of the first edition was its concise review of issues and principles involved in developing an appropriate museum environment. Its weakness was its inability to provide practical answers on how to achieve such an environment that would accommodate the requirements of preservation, aesthetics, and economics. In this regard, suggestions and ideas for solutions were put forth, but not definitive solutions. I hasten to add that this is not so much a weakness of the author, but rather of the reader who may ask for too much from a single, introductory text.

Because the changes in the second edition primarily summarize new practical information rather than alter or add theoretical explanation, those who possess the first edition and use it primarily as a reference text or teaching/learning aid for environmental issues do not need to replace it with the second edition. For those who must make practical decisions on environmental problems and do not have accessor familiarity with recent publications in the conservation literature, the second edition should be useful.

I shall describe briefly a number of the major changes.

1. Summary of Environmental Specifications: In a new appendix, pp. 268–269, Thomson summarizes recommendations made in the body of the text, listing the appropriate page number which discusses the topic. While this summary is extremely useful in its conciseness, I am concerned about how it may be abused. As previously stated, there has been a tendency to use such published values without sufficient reference to the reasoning that lead to these recommendations. Here, where the numbers are completely divorced from the text, such opportunities for misapplication may even be greater.
2. References: The new edition contains a total of 321 references, 61 more than the previous edition. Most of these new citations refer to work published after the first edition. It is a good summary of the literature to date in this field.
3. Light: The limit for illuminance of easel paintings has been changed from 150 lux to 200 lux, based on work done by Loe et al at the Bartlett School of Architecture in London.
4. Relative Humidity: Emphasis on equipment for reading relative humidity has shifted away from the sling psychrometer to electronic hygrometers. Because of advances made in electrical hygrometry, Thomson now accepts the use of this equipment if chosen and used correctly. He specifically mentions one instrument and recommends it for a number of reasons, principally its ability to be recalibrated with a saturated salt. Since there are a number of excellent electronic hygrometers on the market in North America, this specific unit should not be taken as an exclusive recommendation. We await an article that provides clear criteria for choosing any one from the number of competing instruments.In the context of the explanation of hygrometric half-time, Thomson recommends the use of 20 kilograms of silica gel per cubic meter in a showcase. This number is in agreement with his article (Studies In Conservation 28 [1977]: 85-102) differs from his recommendation of 12.5 kilograms in the first edition. Considering the confusion and misunderstandings that this concept has caused among many conservators and exhibition designers, I would have preferred to see the section rewritten to clear up the issue. For example, the 20 kilogram amount is intended for showcases that meet certain conditions, principally: 1) the cases are permanent and will not be maintained and therefore must be self correcting over an annual cycle, 2) the average relative humidity and the extreme high and low fluctuations in RH within the case that are anticipated by this approach are within acceptable limits, 3) the case has a low rate of leakage, and 4) the specific moisture reservoir of the buffer is the same as was used here to derive the 20 kilogram estimate. A change in any of the above conditions could significantly affect the amount needed. For instance, a difference in the moisture reservoir of a buffer from an M value of 2 to 3 accounts for the different recommendations in the first and second edition. From a practical and financial point of view, these numbers are important when planning an exhibition case.The discussion of air conditioning systems has been rewritten to reflect recent advances in variable air volume control designs for mechanical humidity control of buildings. The concept of triple redundancy electronic RH sensors is introduced as the method of monitoring and controlling such a system. While the expanded discussion of mechanical environmental systems is a welcome addition, the whole area is quite foreign to most conservators. Such information should be considered as an introduction, not as a basis for specific recommendations. Again, it is the problem of condensing a subject that requires a book into a few pages.There is a completely revised and improved discussion of RH in “uncontrolled” buildings and a new section on the role of RH and carbon dioxide in caves.
5. Air Pollution: The standard for defining the test for partculate filter efficiency has been revised. A new table listing some materials known to release harmful vapors has been added on page 156. Short sections advocating the use of computers and data logging have been appended to the end of the section on pollution.

There have been dozens of changes between the two editions, principally those summarized above. For an additional listing of changes and discussion, please refer to the review of TheMuseum Environment, second edition, by George Rogers in the IIC-CG Journal.

One section that has barely been revised is Thomson's concluding section entitled “Future Trends in Environmental Control.” The challenge set out by Thomson in 1978 with his first edition remains; it did not require revision. Garry Thomson has made many important contributions to the field, culminating in The Museum Environment. with the publication of the second edition, he continues to provide use with a valuable tool. It has been our mistake to treat his text as the final workbook on the subject, rather than as a means to help us find solutions ourselves. The second edition continues to challenge us to find such solutions.