The Georgia Microscopical Society, a non-profit organization mee'jng at the Fernbank Science Center in Atlanta, Georgia, has sponsored a Young People's Course in Microscopy for a second year. This course, open to high school students, met for 8 sessions on Saturday mornings. The course instructors were Society members from educational, governmental and private institutions who donated their time.

Some 350 years before the invention of photography, Leonardo DaVinci may very well have produced the first photograph - the Shroud of Turin. This extraordinary hypothesis attracted shroud experts Lynn Picknett and Clive Prince, and their efforts to prove or disprove this theory resulted in their recent book Turin Shroud. During their shroud investigations, the authors delved deeply into historical lore, piecing together diverse facts and opinions including those of such figures as the Knights of Templar, alchemists, secret societies, and even Pope innocent VIII. The authors provided convincing evidence that the shroud could have been produced using photograph i c -like techniques that were within the identified capabilities of DaVinci. Most importantly, the authors were able to recreate shroud "look-alike" images with materials and techniques believed to be available to, or devised by, Leonardo DaVinci in the creation of the Turin Shroud.

In high resolution imaging of biologic structure, atomic lorce microscopy (AFM) has been prevailing over scanning tunneling microscopy (STM). This is primarily because biologic materials do not conduct electricity, and STM requires that electrons flow to or from the surface of the specimen, whereas electron flow is not required for AFM. Microscopists intent on using STM have compensated by coating specimens with a thin coat of metal. However, the presence of metal atoms on the surface degrades the resolution. A new development may make STM more useful to biologists than ever before.

A.C. magnetic field (ACMF) sources and their EM interaction mechanisms are discussed in this installment, which continues our July/August series on preventing and resolving site magnetic field problems. This article carries forward the theme of a primer on the basic physical causes and effects of A.C. magnetic fields.with special emphasis on the manner in which such fields may affect site EM instrumentation. Experience has demonstrated that a basic understanding of the various aspects of ACMF sources will often prove helpful in identifying the sources which actually pose a threat to EM site operations.

A new class of SEM has evolved over the past few years which provides some startling capabilities never before available to electron microscopists. These instruments, typically referred to as environmental SEMs or variable pressure SEMs. have opened up a host of new applications that are difficult or impossible with a standard SEM. Many of the constraints of sample preparation and handling that exist with a conventional SEM do not apply to environmental SEMs.

An environmental SEM functions like a conventional SEM except that you can introduce air or any other gas into the chamber and raise the chamber pressure above the normal high vacuum range of 10-5 or 10-6 Torr. Inmost instruments the vacuum can be raised to as much as 1 Torr. This represents a 6 order of magnitude increase in chamber pressure. Environmental SEMs can achieve this high chamber pressure without damage to the electron source by using differential pumping apertures in the column.

Numerous scanned probe microscopes (SPM) have been developed over the past decade. Most are based on the precise positioning of sample and probe using piezoelectric transducers, and some have the capability of imaging flat surfaces with atomic resolution. The first atomic resolution SPM applied to biological samples was the scanning tunneling microscope (STM). The atomic force microscope (AFM) was subsequently developed and over the past few years has become the instrument of choice for biological applications.

When physicists of the last century were studying the nature of light and its application to the newly-refined microscopes, they devised certain laws relating to physical limitations to resolution. These laws had something to do with the wavelength of light being proportional to the limit of resolution. Lately these laws haven't just been broken, they've been shattered! But in all fairness to our predecessors, light is being used now in a manner that they could not have imagined. The scanning interferometric apertureless microscope (SIAM) recently refined by a team led by H. Kumar Wickramasinghe with colleagues Frederic Zenhausern and Yves Martin is a prime example.

In the water bucket analogy (Figure 1), the water level in a bucket represents the Fermi level - the highest occupied energy level in the cathode material. The work function is the energy required to get the “water droplets” (electrons) from the top of the liquid out of the bucket and ever the side (i.e., the distance equivalent to the potential energy barrier).

In photoemission, the energy of a photon can remove an electron at the Fermi level from the cathode material and can impart enough kinetic energy of travel to allow it to escape from the bucket (Figure 1a). In thermionic emission, heat provides the energy to boil the electrons off and out of the bucket (Figure 1b). Finally, in field emission, a high electric field can thin the side of the bucket enough so that the electrons can tunnel right through it (Figure 1c). There are two types of field emission: cold field emission (CFE) and Schottky emission (SE).

This adage for my students was obviously inspired by "He who steals my purse steals trash" but the lens borrower may be in for more serious trouble than the purse snatcher. This comes about because the eyepiece fit and the objective threads are standardized to a couple of standards so that the mechanical interchange of components between different optical microscopes is easily accomplished, while the incompatibility of the optical components is not usually apparent. This incompatibility can range from easily recognized blurring of the image to only slight loss of resolution which leads to inferior work or much wasted time before the problem is recognized.

Scanning probe microscopes (SPMs) designed to fit into scanning elec- tron microscopes (SEMs) are now becoming commercially available and you might ask, "Why would I want to put an SPM in my SEM"? The primary reason is that the too forms of microscope are very complimentary. Each microscope extends the power of the other. The SEM can do things that are hard to do with an SPM, and vice versa.

Not long after the introduction of the STM and the AFM, a few re- searchers built custom SPMs and installed them in their SEMs. The reports of these projects to build hybrid microscopes and examples of the data they produced can be found in the scientific literature.

We are always trying to extend our vision through the four senses of sight, sound, touch and smeil. The microscopy devised by Hooke and Van Leeuwenhoek more than three centuries ago are examples of methods used to extend our visible vision, in fact, instrument designers since then have constructed microscopes using each one of our senses to give us peeks into the microworid. When Robert Hooke took some scrapings from his teeth and viewed the bacteria in these scrapings in his primitive microscope,1 a whole new view of the world ensued. It would, however, have been difficult to predict how microscopy would evolve in the following centuries.