Symmetry and invariance principles have played a vital role in the 
development of physics. And just about as ubiquitous as symmetry is the 
spontaneous breaking of symmetry. In particular, broken symmetry is the 
basic underlying concept of condensed-matter physics. Crystal growth and 
other phase transitions are phenomena involving spontaneous breaking of 
symmetry. Generalised rigidity, as also topological defects like 
dislocations, are some of the consequences of the breaking of symmetry 
involved in the formation of a crystal from the highly symmetric fluid 
phase. The Curie principle, or rather its generalisation called the 
Curie-Shubnikov principle, is the basic symmetry principle of physics. Of 
particular interest is the application of this principle to composite 
objects made up of equal parts (crystals are examples of such composite 
objects because they are made up of equal parts called unit cells). For 
such objects the possibility of the manifestation of a new type of 
symmetry called latent symmetry has been pointed out recently by the 
speaker in his book on ferroic materials. Latent symmetry is that 
unexpected extra symmetry which can arise sometimes when two or more 
identical objects combine to form a composite in a specific way. The 
notion of partial symmetry is familiar in crystallography: it is a local 
symmetry, rather than a global symmetry. Subunits of the object may be 
related by a partial symmetry, but the object as a whole does not have 
that symmetry. By contrast, latent symmetry is that partial symmetry of a 
subunit of the basic components of a composite made up of equal parts 
which is also a global symmetry of the composite.