The history of comet discovery from South Africa is as old as the first settlement by the Dutch at the Cape in 1652. This paper records the discov- ery of 57 comets from South Africa since this time. The most prolific discover- ers are shown to be William Reid and Michiel Bester. Interesting facts relating to the discoverers and their comets are presented. The paper constitutes a sum- mary and is part of a larger ongoing effort by the author to produce a concise historical manuscript of South African comet discovery.

The Leonids is a northern hemisphere shower, which shows periods of enhanced activity coinciding with the return of the parent comet to the Sun's vicinity. These enhanced rates can provide spectacular shows for southern hem- isphere observers provided they coincide with the narrow morning observing window. During the latest set of displays, southern Africa was well placed to observe the fireball peak of 1998 November 17 and the normal peak of 1999 November 18. Other years were badly affected by cloud.

The decay of granite blocks in buildings results in microfracturing, mineral alteration and salt crystallisation. The conservation of granite historic buildings involves the application of cleaning methods to reduce these effects and to improve the general condition of the stone. Strong cleaners applied without any control have sometimes caused damage to the materials. This study determines the effect of various cleaning methods on microfractures, mineralogy and soluble salt content in granite. Samples of weathered granite from buildings in Trinity College, Dublin and unweathered freshly-quarried granite were cleaned by physical and chemical methods. The condition of the granite was assessed before and after cleaning by examining thin sections under a petrographic microscope. Fracturing, mineral transformation and soluble salt content were used as indicators of the condition of the stone. This paper concludes that the cleaning methods tested do not significantly alter the intensity and depth of fracturing in weathered granite. It also concludes that chemical cleaning does not cause significant mineralogical alteration to weathered granite and that salts remaining after cleaning are remnant weathering products and not reaction products. Finally, the paper highlights the effectiveness of a poultice containing detergent and chelating agents in removing salts from weathered granite.

This paper describes the results of the exposure of samples of limestone, sandstone and marble at eight sites around Europe over a 20-month period. A modified microcatchment technique was employed to collect runoff over long time intervals. The sites chosen were in Dublin, Donegal, Manchester, Liphook, Antwerp, Copenhagen, Amsterdam, Padua and Athens. These sites cover a range of environmental conditions from rural to urban. Environmental data on rainfall amount, rainfall acidity, temperature and SO2 were collected for each site. Loss rates were in the same range as reported by other authors for calcareous stones ranging from 12.4 g m−2 year−1 (Padua) to 38.1 g m−2 year−1 (Manchester). The greatest loss was recorded from central Manchester. The Antwerp and Liphook sites also had high loss. Loss at these sites was related to rainfall acidity and SO2 concentrations. Quite high loss was recorded from the rural site. This was found to correspond to unexpectedly high rainfall acidity. The environmental conditions causing stone loss were found to interact in a complex way. Limestone was found to be the least durable of the stones exposed in this study.

Conservation work carried out at Trinity College, Dublin, highlighted problems of decay in granite which is widely regarded as a durable stone. Visual condition assessment of stone work identified an association between decay of granite and the presence of salts. Salt build-up was related to the presence of sources of soluble salts. Mortar joints and limestone features in particular were identified as potential sources of damaging salts. Petrographic analysis of thin sections taken from high and low salt surface environments revealed decay processes typical of granite weathering. Fracturing and chemical alteration of minerals were evident. Decay processes in the sample from the high salt location were more extreme. Analysis of calcium and sulphate in these locations revealed an association between disruption of the stone and high levels of salts. The physical role of mortar in controlling the water movement through the stone is also important in determining where damaging salts are deposited. A new repointing mortar was developed and tested. This mortar has high permeability and flexibility while having a low soluble salt content.

With atmospheric pollution causing building stone to decay at accelerated rates, conservation of historic stone monuments is becoming an increasingly important issue. Mortar joints have a marked effect on how moisture moves in a wall and, hence, on how the wall weathers. Not only does mortar bind stones together, but also a good mortar will prevent the ingress of moisture (and pollutants), enable the buildings to dry out, accommodate movement and will not act as a source of harmful chemicals capable of attacking the surrounding stone. Thus, poor mortar can have deleterious effects on the stonework. This paper, which is the result of research sponsored by the Commission of European Communities, considers a number of commonly used, and some more rarely used, pointing mortars, and assesses them with a view to using the most successful for repointing a historic stone building in Trinity College, Dublin.

With atmospheric pollution causing building stone to decay at accelerated rates, conservation of historic stone monuments is becoming an increasingly important issue. Mortar joints have a marked effect on how moisture moves in a wall and, hence, on how the wall weathers. Not only does mortar bind stones together, but also a good mortar will prevent the ingress of moisture (and pollutants), enable the buildings to dry out, accommodate movement and will not act as a source of harmful chemicals capable of attacking the surrounding stone. Thus, poor mortar can have deleterious effects on the stonework. This paper, which is the result of research sponsored by the Commission of European Communities, considers a number of commonly used, and some more rarely used, pointing mortars, and assesses them with a view to using the most successful for repointing a historic stone building in Trinity College, Dublin.

A method is described for measuring decay rates of carbonate stones over a relatively short time scale (months). The development of this method from flat topped microcatchment units where runoff was collected and analysed is described. The improved unit employs ion exchange resins to collect ions of interest while allowing the bulk of the runoff to flow to waste. The resins can later be eluted in the laboratory to produce figures for stone loss. Initial results for four urban sites around Europe are presented.

The effects of a biocide treatment, pentachlorophenol, and a silicone water repellant on the dissolution processes of limestone were investigated. Limestone microcatchment units were exposed on the pavillion roof of Trinity College, Dublin for a period of 68 days. The effect of the treatment on the chemical composition of runoff from the units was investigated. The pentachlorophenol treatment appeared to cause a decrease in the output of bicarbonate and an increase in the output of nitrite, nitrate and ammonia from the limestone when compared with untreated control stones. These effects are thought to be due to the elimination of biological growth from the stone. The silicone treatment appeared to have decreased the bicarbonate and particulate output relative to the untreated stones. This effect is thought to be due to the decreased residence time of water in the stone.

Techniques of visual analysis and non-destructive testing are being developed as a means of damage assessment of historic building facades.The study's broader objective is the development of a methodology applicable to the stock of European buildings at risk from stone decay. The paper reports the exploratory application of these techniques to a monumental stone building, the Regent's House in Trinity College, Dublin.

Replicated standard 25x25cm square catchments of Massignes limestone were exposed at rooftop height at Trinity College in the centre of Dublin. Each stone was mounted on a large insulated concrete base and inclined at 20° toward the south. All catchments were edged with an upstanding glass kerb. Runoff was collected at the lowest corner into a polypropylene container which was changed daily. One set of three stones and a 'control' copper surface were washed with 500ml distilled water daily and were allowed to drain before the runoff was collected for analysis. Afer filtration solutions were analysed for all detectable inorganic ions on a Dionex ion Chromatograph. There were 38mm of rain on 7 raindays. On one day (7thJune) 16mm fell. The rain pH averaged 6.5. Rain contained significant amounts of Ca++, Mg++, Na+, NH4+, HCO3-, SO4--" and Cl-. Nonetheless dry deposition was the more inportant route of input to microcatchments for Ca++, Mg++, HCO3-", NOx and SO4--". Mass balance budgets on washed stones showed steady losses of Ca++, Mg++and HCO3-, losses with transitory gains of Cl-and SO4--, and gains of K+, NH4+and NO3-. Mass balances of unwashed stones showed losses of Ca+ +, Mg+ +, HCO3", SO4-, NO3-and Cl-, but gains of NH4+.

Serious deterioration in the fabric of historic buildings throughout Europe has necessitated extensive conservation and remedial measures. The conclusions of this study, together with that on the six EC buildings recorded in the Third EC Environmental R+D 1981-85 Programme, suggest that the quality of granite from certain quarries in the Dublin/Wicklow area is variable and that 18th century stone was mainly boulder stone, and stone removed from the upper quarry layers. It has been recorded that this stone, although of inferior quality, was used because it was softer and therefore easier to carve. Cleaning, treating, consolidating and repairing granite of this quality has its difficulties. It does not respond well to consolidation techniques, and attempts at manufacturing repair mortars are not fully satisfactory. No really successful alternative to stone replacement has been discovered.

An hypothesis for the decay of granite in association with sources of Ca in an urban environment is developed. This hypothesis was applied to granite decay in association with limestone decorative features on a facade, and to granite decay in association with mortar joints. The hypothesis was tested by quantitatively comparing the soluble salt content in two facades, one with, the other without, limestone features.