This article is a brief biography and appreciation of the lateM.G.K.Menon, a scientist and administrator of towering abilities,whose seminal role in the development of post-colonialIndian science often gets discounted in comparison with someof his more eye-catching contemporaries. And yet Menon’sachievements stand up to scrutiny as massive and solid as thegranite blocks with which his beloved TIFR is constructed.No scientist in the modern world has played so large and diversea role in setting up scientific studies in his own country,and few individuals in history have ever held such a glitteringsuccession of prestigious positions.

Bertrand’s theorem is one of the landmark results in the contextof the central force problem in mechanics. It leads tothe conditions for closed bound orbits. This pedagogical articleintends to motivate the teacher as well as the student toengage in a formal proof of the theorem. We overview thebasics of central forces and the Abel integral. Thereafter, weobtain the condition for closed orbits. We provide the readerwith a broad panorama of areas/topics where Bertrand’s theoremarises, including interesting scenarios in the regime ofEinstein’s general theory of relativity.

The chemistry behind explosives is marked with the omnipresenceof the element nitrogen. The discovery of the explosiveproperties of nitrogen-based compounds comprises many interestingand serendipitous observations made by inquisitivescientists. In this article, we unravel the fascinating historybehind the development of explosives from the 9th century tothe present. Every country with an army keeps on upgradingthe sharpness and power of their arsenal, and in this regard,the role played by the chemists in developing new explosives,and the chemistry behind these explosives are explained inthis article. The basic chemical properties of explosives, theirclassification, comparison and methods of evaluation are explained.The current status of research in making new explosivesand the challenges involved in making explosive polynitrogencompounds such as pentazolates and pentazenium arealso illustrated.

An annular solar eclipse will be visible on 26th December2019 in parts of Kerala and Tamil Nadu. The annular solareclipse will be fully visible in Coimbatore. In this article,we explore a few basic things about the Earth, Moon, Sunsystem and explain how, why, and when solar eclipses happen.We emphasise that using elementary trigonometry anda simple calculator one can understand many important featuresof solar eclipses. In particular, we estimate the durationof the eclipse and the size of the shadow of the Moon on theEarth.

Continuing to explore the fascinating world of the Indian paperwasp Ropalidia marginata, in this article, we will ask howwasps choose their queens in another context. In the previousarticle in this series, we saw how a simple experiment revealedthat wasps fight, i.e., indulge in dominance-subordinateinteractions, and the winner becomes the queen and theloser becomes the worker. This was in the context of newnest foundation. But contextmatters. When the same waspsonce again have to decide who will be their next queenif the first one dies or is experimentally removed, the samerules do not hold. The wasps in a mature colony continueto show dominance-subordinate interactions and can even bearranged in a dominance hierarchy, but the dominance ranksof the wasps do not predict who their next queen will be.How they choose their next queen in this context continuesto be an enduring mystery. In this article, I will describe foursimple experiments that have helped us come close to nailingthe culprit, although I must confess that we have not yetfound the smoking gun—the chase is on, and we are hot onthe trail—please join in!

The author did not learn probability theory properly when itwas taught to him as an undergraduate. However, now thathe has to teach it has become a fascination. The followingproblem is based on a section in the book Asymptopia by JoelSpencer and Laura Florescu. The original problem had a

“life or death” formulation. This version is less murderous!